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[[File:File:Las_Vegas_slot_machine.jpg|thumb|Las Vegas slot machines]]
A '''slot machine''' ([[American English]]), informally '''fruit machine''' ([[British English]]), '''puggy''' ([[Scottish English]] slang),<ref>{{cite book |last=Partridge |first=Eric |date=2006 |title=''The New Partridge Dictionary of Slang and Unconventional English: J–Z'' |url=https://books.google.com/books?id=mAdUqLrKw4YC&pg=PA1552 |location= |publisher=[[Taylor and Francis]] |page=1552 |isbn=9780415259385 |accessdate=17 October 2014 }}</ref> '''the slots''' ([[Canadian English|Canadian]] and American English), '''poker machine''' (or '''pokies''' in slang) ([[Australian English]] and [[New Zealand English]]) or simply '''slot''' ([[American English]]), is a [[casino]] gambling machine with three or more reels which spin when a button is pushed. Slot machines are also known as '''one-armed bandits''' because they were originally operated by one [[lever]] on the side of the machine as distinct from a button on the front panel and because of their ability to leave the player impoverished or in debt and because ''bandit'' can be a synonym for "thief" in modern usage.<ref>[http://www.oed.com/view/Entry/15149 bandit]
in the Oxford English Dictionary </ref> Many modern machines are still equipped with a legacy lever in addition to the button. 

Slot machines include a [[currency detector]] that validates the money inserted to play. The machine pays off according to patterns of symbols visible on the front of the machine when it stops. Modern computer technology has resulted in variations on the slot machine concept. Slot machines are the most popular gambling method in [[casino]]s and constitute about 70 percent of the average US casino's income.<ref>{{cite web|url=https://www.theatlantic.com/doc/200512/slot-machines|title=How slot machines give gamblers the business|last=Cooper|first=Marc|date=December 2005|publisher=The Atlantic Monthly Group|accessdate=2008-04-21}}</ref>

==Etymology==
The "slot machine" term derives from the slots on the machine for inserting and retrieving coins.<ref>{{cite web|url=http://www.merriam-webster.com/dictionary/slot%20machine|title=Slot Machine - Definition of slot machine by Merriam-Webster|work=merriam-webster.com}}</ref> "Fruit machine" comes from the traditional fruit images on the spinning reels, such as lemons and cherries.<ref>[[OED]], ''fruit,'' n.</ref>

==History==
[[File:Liberty bell.jpg|thumb|1899 "Liberty Bell" machine, manufactured by Charles Fey.]]
[[File:Liberty Bell slot machine 2012-09-15 16-50-38.jpg|thumb|Plaque marking the location of [[Charles Fey|Charles Fey's]] San Francisco workshop, where he invented the three-reel slot machine. The location is a [[California Historical Landmark]].]]
Sittman and Pitt of [[Brooklyn, New York]], U.S. developed a gambling machine in 1891 which was a precursor to the modern slot machine. It contained five drums holding a total of 50 card faces and was based on [[poker]]. This machine proved extremely popular and soon many [[Bar (establishment)|bars]] in the city had one or more of the machines. Players would insert a [[Nickel (U.S. coin)|nickel]] and pull a lever, which would spin the drums and the cards they held, the player hoping for a good poker hand. There was no direct payout mechanism, so a [[Glossary of poker terms|pair of kings]] might get the player a free beer, whereas a [[Glossary of poker terms|royal flush]] could pay out cigars or drinks, the prizes wholly dependent on what was on offer at the local establishment. To make the odds better for the house, two cards were typically removed from the [[Deck (cards)|deck]]: the ten of [[Spades (suit)|spades]] and the [[Jack (playing card)|jack of hearts]], which doubles the [[odds]] against winning a royal flush. The drums could also be rearranged to further reduce a player's chance of winning.

Due to the vast number of possible wins with the original poker card based game, it proved practically impossible to come up with a way to make a machine capable of making an automatic payout for all possible winning combinations. Somewhere between 1887 and 1895,<ref>{{cite web|url=http://www.slot-machine-resource.com/slot-machine-history.htm |title=History of slot machines }}</ref>  [[Charles Fey]] of [[San Francisco, California]], U.S. devised a much simpler automatic mechanism<ref>{{cite web|url=http://casinogambling.about.com/od/slots/a/charlesfey.htm |title=Charles Fey article |publisher=Casinogambling.about.com |date=2009-06-22 |accessdate=2009-08-04}}</ref> with three spinning reels containing a total of five symbols – horseshoes, diamonds, spades, hearts, and a [[Liberty Bell]]. The bell gave the machine its name. By replacing ten cards with five symbols and using three reels instead of five drums, the complexity of reading a win was considerably reduced, allowing Fey to devise an effective automatic payout mechanism. Three bells in a row produced the biggest payoff, ten nickels (50¢). ''Liberty Bell'' was a huge success and spawned a thriving mechanical gaming device industry. Even when the use of these gambling devices was banned in his home state after a few years, Fey still couldn't keep up with demand for the game elsewhere. The Liberty Bell machine was so popular that it was copied by many slot machine manufacturers. Thus in 1907, manufacturer Herbert Mills from Chicago produced a slot machine called the Operator Bell. By 1908 lots of "bell" machines were installed in most cigar stores, saloons, bowling alleys, brothels and barber shops.<ref>{{cite web|url=http://indiancountrytodaymedianetwork.com/gallery/photo/long-colorful-profitable-history-slot-machines-55000 |title=The Long, Colorful, Profitable History of Slot Machines |publisher=The Indian Observer |accessdate=2016-07-18}}</ref> Early machines, including an 1899 "Liberty Bell", are now part of the Nevada State Museum's Fey Collection.<ref>{{Cite web|title = CM-5716-P-06 Machine, Slot|url = http://www.nevadaculture.org/museums/new_exhibits/cc-slot_machines/exhibit1/e10007a.html|website = Nevada State Museum|accessdate = 2015-09-18}}</ref>

Other early machines, such as the [[trade stimulator]], gave out winnings in the form of fruit-flavoured [[chewing gum]]s with pictures of the flavours as symbols on the reels. The popular cherry and melon symbols derive from this machine. The BAR symbol now common in slot machines was derived from an early logo of the [[Bell-Fruit Gum Company]]. The payment of food prizes was a commonly used technique to avoid laws against gambling in a number of states, and for this reason a number of [[gumball machine|gumball]] and other [[vending machine]]s were regarded with mistrust by the courts. The two [[Iowa]] cases of ''State v. Ellis''<ref>200 Iowa 1228, 206 N.W. 105. (Iowa, 1925).</ref> and ''State v. Striggles''<ref>202 Iowa 1318, 210 N.W. 137. (Iowa, 1926).</ref> are both used in classes on [[criminal law]] to illustrate the concept of reliance upon authority as it relates to the axiomatic ''[[ignorantia juris non excusat]]'' ("ignorance of the law is no excuse").<ref>Singer, Richard G. ''[http://wings.buffalo.edu/law/bclc/bclrarticles/3(2)/singer.pdf The Proposed Duty to Inquire as Affected by Recent Criminal Law Decisions in the United States Supreme Court] {{webarchive|url=https://web.archive.org/web/20081219143750/http://wings.buffalo.edu/law/bclc/bclrarticles/3%282%29/singer.pdf |date=2008-12-19 }}''. 24 April 2000.</ref> In these cases, a [[Mint (candy)|mint]] vending machine was declared to be a gambling device because by (internally manufactured) chance the machine would occasionally give the next user a number of tokens exchangeable for more candy. Despite the fact that the result of the next use would be displayed on the machine, the courts ruled that "[t]he machine appealed to the player's propensity to gamble, and that is [a] vice."<ref>''State v. Ellis''. 200 Iowa 1228, 206 N.W. 105. (Iowa, 1925). (citing to ''Ferguson v. State of Indiana'', 178 Ind. 568, 99 N. E. 806 (1912); ''City of Moberly v. Deskin'', 169 Mo. App. 672, 155 S. W. 842. (1913).)</ref>

In 1963, [[Bally Manufacturing|Bally]] developed the first fully electromechanical slot machine, called ''Money Honey'' (although earlier machines such as the ''High Hand'' draw poker machine by Bally had exhibited the basics of electromechanical construction as early as 1940). The electromechanical approach of the 1960s allowed Money Honey to be the first slot machine with a bottomless hopper and automatic payout of up to 500 coins without the help of an attendant.<ref>{{cite web|url=http://ballytech.com/company-information |title=Bally Technologies, Inc. &#124; Company Information |publisher=Ballytech.com |date= |accessdate=2009-08-04}}</ref> The popularity of this machine led to the increasing predominance of [[electronic game]]s, and the side lever soon became vestigial.

The first true video slot machine was developed in 1976 in [[Kearny Mesa, California]] by the Las-Vegas based Fortune Coin Co. This slot machine used a modified {{convert|19|in|cm|adj=on}} Sony Trinitron color receiver for the display and logic boards for all slot machine functions. The prototype was mounted in a full size show-ready slot machine cabinet. The first production units went on trial in the [[Las Vegas Hilton Hotel]]. After some "cheat-proofing" modifications, the video slot machine was approved by the Nevada State Gaming Commission and eventually found popularity in the [[Las Vegas Strip]] and downtown casinos. Fortune Coin Co. and their video slot machine technology were purchased by IGT (International Gaming Technology) in 1978.{{Citation needed|date=September 2015}}

The first American video slot machine to offer a "second screen" bonus round was ''Reel 'Em In'' developed by [[WMS Industries Inc.]] in 1996.<ref>{{cite web|url=http://www.casinocenter.com/?p=834|title=HALL OF FAME IN SLOT GAMES  : Casino Player Magazine - Strictly Slots Magazine - Casino Gambling Tips|work=casinocenter.com}}</ref> This type of machine had appeared in Australia from at least 1994 with the "Three Bags Full" game.<ref>{{cite web|url=http://www.arcade-history.com/?n=3-bags-full&page=detail&id=5056|title=3 Bags Full|work=arcade-history.com}}</ref> In this type of machine, the display changes to provide a different game where an additional payout may be won or accumulated.

==Description==
[[Image:Vegas slots.JPG|left|thumb|A row of "Wheel of Fortune" slot machines in a casino in Las Vegas. This specific slot machine is themed to the TV game show ''[[Wheel of Fortune (U.S. game show)|Wheel of Fortune]]''.]]

A person playing a slot machine can insert cash, or in [[ticket-in, ticket-out]] machines, a paper ticket with a [[barcode]], into a designated slot on the machine. The machine is then activated by means of a lever or button, or on newer machines, by pressing a touchscreen on its face. The game itself may or may not involve [[skill]] on the player's part &mdash; or it may create the [[illusion]] of involving skill while only being a [[game of chance]].

The object of the game is to win money from the machine. The game usually involves matching symbols, either on mechanical reels that spin and stop to reveal one or several symbols, or on simulated reels shown on a video screen. The symbols are usually brightly colored and easily recognizable, such as images of fruits, numerals or letters, and simple shapes such as bells, diamonds, or hearts; newer video slot machines use animated cartoon characters and images of popular actors or singers (in the case of themed slot machines, as described below).

Most games have a variety of winning combination of symbols, often posted on the face of the machine (or available on a different screen, accessible by touching a button on the main touchscreen, on video slot machines). If a player matches a combination according to the rules of the game, the slot machine credits the player cash or some other sort of value, such as free spins or extra games. Free spins are a common feature in modern slot games allowing the user to spin the machine's reels without charge. Many [[online casino]]s advertise their free spin rewards and emphasize this feature.

There are many different kinds of gambling slot machines in places such as Las Vegas (as well as casinos modeled after those in Las Vegas, including those operated on Native American reservations). Some of the most popular are the [[video poker]] machines, in which players hope to obtain a set of symbols corresponding to a winning [[poker]] hand. Depending on the machine, players can play one, 100, or more hands at one time. Another popular type of machine internationally are [[video bingo]] machines, where a player can play Latin style bingo or American style bingo. Depending on the machine players can play one bingo card or more at a time.<ref>{{cite web|url=http://ggbmagazine.com/issue/vol-13-no-5-may-2014/article/bingo-tech|title=Bingo Tech -    Global Gaming Business Magazine|work=ggbmagazine.com}}</ref>

Multi-line slot machines have become more popular since the 1990s. These machines have more than one payline, meaning that visible symbols that are not aligned on the main horizontal may be considered for winning combinations. Reel slot machines commonly have three or five paylines, while video slot machines may have 9, 15, 25, or as many as 243 different paylines. Most video slot machines have a themed game, some of which feature graphics and music based on popular entertainers, motion pictures or TV programs (''[[The Addams Family (1964 TV series)|The Addams Family]]'', ''[[I Dream of Jeannie]]'', ''[[Happy Days]]'', etc.) with a bonus round. Most accept variable numbers of credits to play, with 1 to 15 credits per line being typical. The higher the amount bet, the higher the payout will be if the player wins.

There are also standard 3 to 5 reel electromechanical machines, of various types. These are the typical "one-armed bandits." Since about 2005 there have been hybrid machines introduced, which combine elements of both video machines and traditional electromechanical machines.

One of the main differences between video slot machines and reel machines is in the way payouts are calculated. With reel machines, the only way to win the maximum jackpot is to play the maximum number of coins (usually 3, sometimes 4, or even 5 coins per spin). With video machines, the fixed payout values are multiplied by the number of coins per line that is being bet. In other words: on a reel machine, the odds are less unfavorable if the gambler plays with the maximum number of coins available.<ref>{{cite web|last1=Harris|first1=Tom|title=How Slot Machines Work|url=http://entertainment.howstuffworks.com/slot-machine4.htm|accessdate=10 July 2014}}</ref>

As an example, on the ''Wheel of Fortune'' reel machine (based on the popular ''[[Wheel of Fortune (U.S. game show)|Wheel of Fortune]]'' TV game show created by [[Merv Griffin]]), the player must play 3 coins per spin to be eligible to trigger the bonus round and possibly win the jackpot. On the Wheel of Fortune video machine, the chances of triggering the bonus round or winning the maximum jackpot are exactly the same regardless of the number of coins bet on each line.

Larger casinos offer slot machines with denominations from 1 cent ("penny slots") all the way up to $100.00 or more per credit. Large denomination slot machines are usually cordoned off from the rest of the casino into a "High Limit" area, often with a separate team of attendants to cater to the needs of those who play there.

In the last few years, new '''multi-denomination''' slot machines have been introduced. With these slot machines, the player can choose the value of each credit wagered (the '''stake''') from a list of options. Based upon the player's selection, the slot machine automatically calculates the number of credits the player receives in exchange for the cash inserted and displays the number of available credits to the player.

==Terminology==
'''Bonus''' is a special feature of the particular game theme, which is activated when certain symbols appear in a winning combination. Bonuses vary depending upon the game. Some bonus rounds are a special session of free spins (the number of which is often based on the winning combination that triggers the bonus), often with a different or modified set of winning combinations as the main game, and often with winning credit values increased by a specific multiplier, which is prominently displayed as part of the bonus graphics and/or animation (which in many cases is of a slightly different design or color scheme from the main game). In other bonus rounds, the player is presented with several items on a screen from which to choose. As the player chooses items, a number of credits is revealed and awarded. Some bonuses use a mechanical device, such as a spinning wheel, that works in conjunction with the bonus to display the amount won. (Some machines feature two or more of these bonus styles as part of the same game.)

'''Candle''' is a light on top of the slot machine. It flashes to alert the operator that change is needed, hand pay is requested or a potential problem with the machine. It can be lit by the player by pressing the "service" or "help" button.

'''Carousel''' refers to a grouping of slot machines, usually in a circle or oval formation.

'''Coin hopper''' is a container where the coins that are immediately available for payouts are held. The hopper is a mechanical device that rotates coins into the coin tray when a player collects credits/coins (by pressing a "Cash Out" button). When a certain preset coin capacity is reached, a coin diverter automatically redirects, or "drops," excess coins into a "drop bucket" or "drop box." (Unused coin hoppers can still be found even on games that exclusively employ Ticket-In Ticket-Out technology, as a vestige.)

'''Credit meter''' is a visual [[Light-emitting diode|LED]] display of the amount of money or number of credits on the machine. On video reel machines this is either a simulated LED display, or represented in a different font altogether, based on the design of the game graphics.

'''Drop bucket''' or '''drop box''' is a container located in a slot machine's base where excess coins are diverted from the hopper. Typically, a drop bucket is used for low denomination slot machines and a drop box is used for high denomination slot machines. A drop box contains a hinged lid with one or more locks whereas a drop bucket does not contain a lid. The contents of drop buckets and drop boxes are collected and [[hard count|counted]] by the casino on a scheduled basis.

'''EGM''' is used as a shorthand for "Electronic Gaming Machine."

'''Free Spin''' Free Spin is a term used in video slot games and online slot games to specify that the spin will be completed without a charge or on the same wager. Free spins can get triggered by a number of things, each game use a different method. Usually, landing a number of special symbols on reels is required to activate the free spins bonus round. Mostly scatter symbols are preferred for this activation, although wild symbols (or a completely different symbol dedicated for this feature) can be used too. In most slot games, landing at least three special symbols on reels is mandatory to trigger the feature. Once triggered, free spins bonus round award a number of spins free of charge to the player. The number of free spins differ from game to game, and can be 5 or 50. The spins are automatically used by the game and the player keeps any profit after the spins are complete.

'''[[Hand pay]]''' refers to a payout made by an attendant or at an exchange point ("cage"), rather than by the slot machine itself. A hand pay occurs when the amount of the payout exceeds the maximum amount that was preset by the slot machine's operator. Usually, the maximum amount is set at the level where the operator must begin to deduct taxes. A hand pay could also be necessary as a result of a short pay.

'''Hopper fill slip''' is a document used to record the replenishment of the coin in the coin hopper after it becomes depleted as a result of making payouts to players. The slip indicates the amount of coin placed into the hoppers, as well as the signatures of the employees involved in the transaction, the slot machine number and the location and the date.

'''MEAL book''' ('''''M'''''achine '''''e'''''ntry '''''a'''''uthorization '''''l'''''og)  is a log of the employee's entries into the machine

'''Low Level''' or '''Slant Top''' slot machines include a stool so the player has sitdown access. '''Stand Up''' or '''Upright''' slot machines are played while standing.

'''Optimal play''' is a payback percentage based on a gambler using the optimal strategy in a skill-based slot machine game.

'''Payline''' is a line that crosses through one symbol on each reel, along which a winning combination is evaluated. Classic spinning reel machines usually have up to nine paylines, while video slot machines may have as many as one hundred. Paylines could be of various shapes (horizontal, vertical, oblique, triangular, zigzag, etc.)

'''Rollup''' is the process of dramatizing a win by playing sounds while the '''meters''' count up to the amount that has been won.

'''Short pay''' refers to a partial payout made by a slot machine, which is less than the amount due to the player. This occurs if the coin hopper has been depleted as a result of making earlier payouts to players. The remaining amount due to the player is either paid as a hand pay or an attendant will come and refill the machine.

'''Scatter Symbol''' It is required to place at least two of the same symbols on a pay line to get paid in slot games. However, scatter symbols work differently and award a prize whether they are placed on a pay line or not. But the player still needs to get at least two of them in modern slot games. (The more, the better.) Scatter symbols are usually used to award a number of free spins. The number of free spins differs from game to game; i.e. 20 free spins for landing 3 scatter symbols anywhere on reels. They can also award coin prizes, based on their number. The prizes are usually small, but they are paid in addition to other winnings. Scatter symbol is a special symbol, which means the wild symbol cannot replace it.

'''Slot Variance ''' At the heart of slot machine gameplay is the concept of slot variance (or slot volatility) that is fundamental to how a slot machine ‘feels’ to play. Slot variance is a measure of risk associated with playing a slot machine. A low variance slot machine has regular but smaller wins and a high variance slot machine has fewer but bigger wins.<ref>http://www.online-slots.casino/guides-and-info/slot-variance/</ref>

'''Taste''' is a reference to the small amount often paid out to keep a player seated and continuously betting. Only rarely will machines fail to pay out even the minimum placed a bet over the course of several pulls.

[[Image:Slot machine Tilt error.jpg|right|thumb|Display screen of a slot machine in tilt mode]]
'''Tilt'''
Electromechanical slot machines usually include an electromechanical "[[mercury switch|tilt switch]]", which makes or breaks a circuit if the machine is tilted or otherwise tampered with, and so triggers an alarm. While modern machines no longer have tilt switches, any kind of technical fault (door switch in the wrong state, reel motor failure, out of paper, etc.) is still called a "tilt".

'''Theoretical Hold Worksheet'''
A document provided by the manufacturer for all slot machines, which indicates the theoretical percentage that the slot machine should hold based on the amount paid in. The worksheet also indicates the reel strip settings, number of coins that may be played, the payout schedule, the number of reels and other information descriptive of the particular type of slot machine.

'''Weight count''' is an American term, referring to the dollar amount of coins or tokens removed from a slot machine's drop bucket or drop box and counted by the casino's [[hard count]] team through the use of a weigh scale.

'''Wild Symbol''' Wild symbols act like joker cards in a slot game. Basically, they substitute for all other symbols in the game, usually except for other special symbols, such as scatter and jackpot. They can appear on any of the reels. However, this is not mandatory and can be changed from game to game. In some games, wild symbols can appear only on certain reels. Or, they can appear only during the bonus rounds. The player must refer to the rules and paytable of the game to learn about the landing rules. In online slot games, they can also be used for winning a jackpot, multiplying the prize and/or triggering a certain feature.

'''Mobile''' is when the slot machine is hosted for [[online gambling]] and it is usually available for use on a phone, tablet, or other portable device. These are often standalone mobile casino applications but are also found as part of the online casino site. See [[Mobile gambling]].

==Pay table==
{{Main article|Pay table}}
Each machine has a table that lists the number of credits the player will receive if the symbols listed on the pay table line up on the pay line of the machine. Some symbols are wild and can represent many, or all, of the other symbols to complete a winning line. Especially on older machines, the pay table is listed on the face of the machine, usually above and below the area containing the wheels. Most video machines display the pay table when the player presses a "pay table" button or touches "pay table" on the screen; some have the pay table listed on the cabinet as well.

==Technology==

===Reels===
[[File:Slot Machine Las Vegas (5421764876).jpg|thumb|Three reels of a slot machine]]
Historically, all slot machines used revolving mechanical reels to display and determine results. Although the original slot machine used five reels, simpler, and therefore more reliable, three reel machines quickly became the standard.

A problem with three reel machines is that the number of combinations is only [[cube (algebra)|cubic]] &ndash; the original slot machine with three physical reels and 10 symbols on each reel had only 10<sup>3</sup> = 1,000 possible combinations. This limited the manufacturer's ability to offer large jackpots since even the rarest event had a likelihood of 0.1%. The maximum theoretical payout, assuming 100% return to player would be 1000 times the bet, but that would leave no room for other pays, making the machine very high risk, and also quite boring.

Although the number of symbols eventually increased to about 22, allowing 10,648 combinations,<ref>http://gaming.unlv.edu/reading/Pacyniak.PDF</ref> this still limited jackpot sizes as well as the number of possible outcomes.

In the 1980s, however, slot machine manufacturers incorporated electronics into their products and programmed them to weight particular symbols. Thus the odds of losing symbols appearing on the payline became disproportionate to their actual frequency on the physical reel. A symbol would only appear once on the reel displayed to the player, but could, in fact, occupy several stops on the multiple reel.

In 1984 Inge Telnaes received a patent for a device titled, "Electronic Gaming Device Utilizing a Random Number Generator for Selecting the Reel Stop Positions" (US Patent 4448419),<ref>{{US patent|4448419|Electronic gaming device utilizing a random number generator for selecting the reel stop positions}}</ref> which states: "It is important to make a machine that is perceived to present greater chances of payoff than it actually has within the legal limitations that games of chance must operate." <ref>
{{cite journal
 |last=Collier |first=Roger
 |date=1 July 2008
 |title=Do slot machines play mind games with gamblers?
 |journal=Canadian Medical Association Journal
 |volume=179 |issue=1 |pages=23–4
 |doi=10.1503/cmaj.080870
 |pmc=2464464
 |pmid=18591518
}}</ref>  The patent was later bought by [[International Game Technology (1975)|International Game Technology]] and has since expired.

A virtual reel that has 256 virtual stops per reel would allow up to 256<sup>3</sup> = 16,777,216 final positions. The manufacturer could choose to offer a million dollar jackpot from a $1 bet, confident that it will only happen, over the long term, once every 16.8 million plays.

===Computerization===
With [[microprocessor]]s now ubiquitous, the computers inside modern slot machines allow manufacturers to assign a different probability to every symbol on every reel. To the player it might appear that a winning symbol was 'so close', whereas in fact the probability is much lower.

In modern slot machines, the reels and lever are for historical and entertainment reasons only.

In the 1980s in the UK machines embodying microprocessors became common.
These used a number of features to ensure the payout was controlled within the limits of the gambling legislation.
As the coin was inserted into the machine it could go one of two routes, either direct into the cashbox for the benefit of the owner, or alternatively it would go into a channel that formed the payout reservoir, the microprocessor monitoring the number of coins in this channel.
The drums themselves were driven by stepper motors, controlled by the processor and with proximity sensors monitoring the position of the drums.
A "look up table" within the software allows the processor to know what symbols were being displayed on the drums to the gambler.
This allowed the system to control the level of payout by stopping the drums at positions it had determined.
If the payout channel had filled up, the payout became more generous, if nearly empty, less so thus giving good control of the odds.

===Video slot machines===
The video slot machine is a more recent innovation, with no moving parts at all &ndash; instead a graphical representation of one appears on screen. Since the player is essentially playing a [[PC game|computer]]/[[video game]], the manufacturers are able to offer more interactive elements, such as advanced bonus games and advanced video graphics.

In addition, because there are no mechanical constraints on the design of video slot machines, most display five reels rather than three. This greatly expands the number of possibilities: a machine can have 50 or more symbols on a reel, giving [[odds]] as high as 300 million to 1 against &ndash; enough for even the largest jackpot. As there are so many combinations given by five reels, the manufacturers do not need to weight the payout symbols (although some may still do so). Instead, higher paying symbols will typically appear only once or twice on each reel, while more common symbols, earning a more frequent payout, will appear many times.

Video slot machines typically encourage the player to play multiple "lines", so rather than simply taking the middle of the three symbols displayed on each reel, a line could go from top left to bottom right, or any of the other patterns specified by the manufacturer. As each symbol is equally likely, there is no difficulty for the manufacturer in allowing the player to take any or all of the possible lines on offer &ndash; the long-term return to player will be the same. The difference for the player is that the more lines he plays the more likely he is to get paid on a given spin &ndash;  though of course he is betting more in the first place.

To avoid the feeling that the player's money is simply ebbing away (whereas a payout of 100 credits on a single line machine would be 100 bets, and the player would feel they had made a substantial win, on a 20 line machine, it would only be 5 bets and would not seem significant), manufacturers commonly offer bonus games, which can return many times their bet. The player is encouraged to keep playing to reach the bonus: even if he is losing, the bonus game could allow him to win back his losses.

===Random number generators===
All modern machines are designed using [[pseudo random number generator]]s ("PRNGs"), which are constantly generating a sequence of simulated random numbers, at a rate of hundreds or perhaps thousands per second. As soon as the "Play" button is pressed, the most recent random number is used to determine the result. This means that the result varies depending on exactly when the game is played. A fraction of a second earlier or later, and the result would be different.

It is important that the machine contains a high-quality RNG implementation, because all PRNGs must eventually repeat their number sequence,<ref>{{cite book|title=[[Art of Computer Programming]]|volume=II. Seminumerical Algorithms|edition=1st|chapter=3. Random numbers|last=Knuth|first=Donald E.|authorlink=Donald Knuth|date=|pp=3–4}}</ref> and if the period is short, or the PRNG is otherwise flawed, an advanced player may be able to 'predict' the next result. Having access to the PRNG code and seed values, [[Ronald Dale Harris]], a former slot machine programmer, discovered equations for specific gambling games like [[Keno]] that allowed him to predict what the next set of selected numbers would be based on the previous games played.

Most machines are designed to defeat this by generating numbers even when the machine is not being played, so the player cannot tell where in the sequence they are, even if he knows how the machine was programmed.

===Payout percentage===
Slot machines are typically programmed to pay out as winnings 82% to 98% of the money that is wagered by players. This is known as the "theoretical payout percentage" or RTP, "return to player". The minimum theoretical payout percentage varies among jurisdictions and is typically established by law or regulation. For example, the minimum payout in [[Nevada]] is 75%, in [[New Jersey]], 83%, and in Mississippi 80%. The winning patterns on slot machines &ndash; the amounts they pay and the frequencies of those payouts &ndash; are carefully selected to yield a certain fraction of the money played to the "house" (the operator of the slot machine), while returning the rest to the players during play. Suppose that a certain slot machine costs $1 per spin and has a return to player (RTP) of 95%. It can be calculated that over a sufficiently long period, such as 1,000,000 spins, that the machine will return an average of $950,000 to its players, who have inserted $1,000,000 during that time. In this (simplified) example, the slot machine is said to pay out 95%. The operator keeps the remaining $50,000. Within some EGM development organizations this concept is referred to simply as "par." "Par" also manifests itself to gamblers as promotional techniques: "Our 'Loose Slots' have a 93% payback! Play now!" It is worth noting that the "Loose Slots" actually may describe a very few anonymous machines in a particular bank of EGMs.

A slot machine's theoretical payout percentage is set at the factory when the [[software]] is written. Changing the payout percentage after a slot machine has been placed on the gaming floor requires a physical swap of the software or ''[[firmware]]'', which is usually stored on an [[EPROM]] but may be loaded onto non-volatile random access memory ([[NVRAM]]) or even stored on [[CD-ROM]] or [[DVD]], depending on the capabilities of the machine and the applicable regulations. Based on current technology, this is a time-consuming process and as such is done infrequently. In certain jurisdictions, such as New Jersey, the EPROM has a [[tamper-evident]] [[security seal|seal]] and can only be changed in the presence of [[Gaming Control Board]] officials. Other jurisdictions, including Nevada, randomly [[audit]] slot machines to ensure that they contain only approved software.

Historically, many casinos, both online and offline, have been unwilling to publish individual game RTP figures, making it impossible for the player to know whether they are playing a "loose" or a "tight" game. Since the turn of the century some information regarding these figures has started to come into the public domain either through various casinos releasing them - primarily this applies to online casino - or through studies by independent gambling authorities.<ref name="woolvodds">{{cite web |url=http://wizardofodds.com/games/slots/appendix/3a/ |title=The Wizard of Odds - Slots Machine Odds in Las Vegas |date=13 February 2003  |author=Michael Shackleford }}</ref>

The ''return to player'' is not the only statistic that is of interest. The probabilities of every payout on the pay table is also critical. For example, consider a hypothetical slot machine with a dozen different values on the pay table. However, the probabilities of getting all the payouts are zero except the largest one. If the payout is 4,000 times the input amount, and it happens every 4,000 times on average, the ''return to player'' is exactly 100%, but the game would be dull to play. Also, most people would not win anything, and having entries on the paytable that have a return of zero would be deceptive. As these individual probabilities are closely guarded secrets, it is possible that the advertised machines with high return to player simply increase the probabilities of these jackpots. The casino could legally place machines of a similar style payout and advertise that some machines have 100% return to player. The added advantage is that these large jackpots increase the excitement of the other players.

The table of probabilities for a specific machine is called the Probability and Accounting Report or PAR sheet, also PARS commonly understood as Paytable and Reel Strips. Mathematician [[Michael Shackleford]] revealed the PARS for one commercial slot machine, an original [[International Gaming Technology]] ''Red White and Blue'' machine. This game, in its original form, is obsolete, so these specific probabilities do not apply. He only published the odds after a fan of his sent him some information provided on a slot machine that was posted on a machine in the Netherlands. The psychology of the machine design is quickly revealed. There are 13 possible payouts ranging from 1:1 to 2,400:1. The 1:1 payout comes every 8 plays. The 5:1 payout comes every 33 plays, whereas the 2:1 payout comes every 600 plays. Most players assume the likelihood increases proportionate to the payout. The one midsize payout that is designed to give the player a thrill is the 80:1 payout. It is programmed to occur an average of once every 219 plays. The 80:1 payout is high enough to create excitement, but not high enough that it makes it likely that the player will take his winnings and abandon the game. More than likely the player began the game with at least 80 times his bet (for instance there are 80 quarters in $20). In contrast the 150:1 payout occurs only on average of once every 6,241 plays. The highest payout of 2,400:1 occurs only on average of once every 64<sup>3</sup>=262,144 plays since the machine has 64 virtual stops. The player who continues to feed the machine is likely to have several midsize payouts, but unlikely to have a large payout. He quits after he is bored or has exhausted his bankroll.<ref>{{cite web |url=http://wizardofodds.com/slots/ |title=Wizard of Odds- Slot machines explained }}</ref>

Despite the fact that they are confidential, occasionally a PAR sheet is posted on a website. They have limited value to the player, because usually a machine will have 8 to 12 different possible programs with varying payouts. In addition, slight variations of each machine (e.g., with ''double jackpots'' or ''five times play'') are always being developed. The casino operator can choose which EPROM chip to install in any particular machine to select the payout desired. The result is that there is not really such a thing as a high payback type of machine, since every machine potentially has multiple settings. From October 2001 to February 2002, columnist Michael Shackleford obtained PAR sheets for five different nickel machines; four IGT games ''[[Austin Powers (disambiguation)|Austin Powers]]'', ''Fortune Cookie'', ''Leopard Spots'' and ''[[Wheel of Fortune (U.S. game show)|Wheel of Fortune]]'' and one game manufactured by WMS; ''Reel 'em In''. Without revealing the proprietary information, he developed a program that would allow him to determine with usually less than a dozen plays on each machine which EPROM chip was installed. Then he did a survey of over 400 machines in 70 different casinos in Las Vegas. He averaged the data, and assigned an average payback percentage to the machines in each casino. The resultant list was widely publicized for marketing purposes (especially by the Palms casino which had the top ranking).<ref name="woolvodds" />

One reason that the slot machine is so profitable to a casino is that the player must play the ''high house edge and high payout'' wagers along with the ''low house edge and low payout'' wagers. In a more traditional wagering game like craps, the player knows that certain wagers have almost a 50/50 chance of winning or losing, but they only pay a limited multiple of the original bet (usually no higher than three times). Other bets have a higher house edge, but the player is rewarded with a bigger win (up to thirty times in craps). The player can choose what kind of wager he wants to make. A slot machine does not afford such an opportunity. Theoretically, the operator could make these probabilities available, or allow the player to choose which one so that the player is free to make a choice. However, no operator has ever enacted this strategy. Different machines have different maximum payouts, but without knowing the odds of getting the jackpot, there is no rational way to differentiate.

In many markets where central monitoring and control systems are used to link machines for auditing and security purposes, usually in wide area networks of multiple venues and thousands of machines, player return must usually be changed from a central computer rather than at each machine. A range of percentages is set in the game software and selected remotely.

In 2006, the Nevada Gaming Commission began working with Las Vegas casinos on technology that would allow the casino's management to change the game, the odds, and the payouts remotely. The change cannot be done instantaneously, but only after the selected machine has been idle for at least four minutes. After the change is made, the machine must be locked to new players for four minutes and display an on-screen message informing potential players that a change is being made.<ref>{{cite news|last=Richtel |first=Matt |url=https://www.nytimes.com/2006/04/12/technology/12casino.html?ei=5089&en=9e945a28ba5016c6&ex=1302494400&partner=rssyahoo&emc=rss&pagewanted=all |title=From the Back Office, a Casino Can Change the Slot Machine in Seconds|newspaper=[[New York Times]]|date=12 April 2009|accessdate=10 December 2009}}</ref>

===Linked machines===
Often machines are linked together in a way that allows a group of machines to offer a particularly large prize, or "jackpot". Each slot machine in the group contributes a small amount to this [[progressive jackpot]], awarded to a player who gets, for example, a royal flush on a video poker machine or a specific combination of symbols on a regular or nine-line slot machine. The amount paid for the progressive jackpot is usually far higher than any single slot machine could pay on its own.

In some cases multiple machines are linked across multiple casinos. In these cases, the machines may be owned by the manufacturer, who is responsible for paying the jackpot. The casinos [[lease]] the machines rather than owning them outright.

Casinos in New Jersey, Nevada, and [[South Dakota]] now offer multi-state progressive jackpots, which now offer bigger jackpot pools.<ref>{{cite web|title=Division of Gaming Enforcement Announces Approval for Interstate Progressive Slot Machines|url=http://www.nj.gov/oag/ge/2014news/MultistateProgressiveSlotMachines.pdf|website=New Jersey Division of Gaming Enforcement}}</ref><ref>{{cite web|title=Division of Gaming Enforcement Announces Interstate Progressive Slots Link with Nevada|url=http://www.nj.gov/oag/ge/2014news/Multistate%20ProgressiveSlots.pdf|website=New Jersey Division of Gaming Enforcement}}</ref>

===Fraud===
Mechanical slot machines and their coin acceptors were sometimes susceptible to cheating devices and other scams. One historical example involved spinning a coin with a short length of plastic wire. The weight and size of the coin would be accepted by the machine and credits would be granted. However, the spin created by the plastic wire would cause the coin to exit through the reject chute into the payout tray. This particular scam has become obsolete due to improvements in newer slot machines. Another obsolete method of defeating slot machines was to use a light source to confuse the optical sensor used to count coins during payout.<ref>{{cite web|url=http://usatoday30.usatoday.com/tech/news/2003-08-11-slot-cheats_x.htm |title=Slot machine cheat bilked casinos with ingenious gadgets |publisher=USAToday.com |accessdate=2014-06-08}}</ref>

Modern slot machines are controlled by EPROM computer chips and, in large casinos, coin acceptors have become obsolete in favor of bill acceptors. These machines and their bill acceptors are designed with advanced anti-cheating and anti-counterfeiting measures and are difficult to defraud. Early computerized slot machines were sometimes defrauded through the use of cheating devices, such as the "slider" or "monkey paw".  Computerized slot machines are fully deterministic and thus outcomes can be sometimes successfully predicted.<ref>{{cite news|last1=Koerner|first1=Brendan|title=Russians Engineer a Brilliant Slot Machine Cheat—And Casinos Have No Fix|url=https://www.wired.com/2017/02/russians-engineer-brilliant-slot-machine-cheat-casinos-no-fix|accessdate=7 February 2017|work=[[Wired (magazine)|Wired]]|date=8 February 2017}}</ref>

===Jackpot errors===
Malfunctioning electronic slot machines are capable of indicating jackpot winnings far in excess of those advertised.<ref>{{cite web|url=http://wcfcourier.com/news/local/woman-sues-isle-after-she-s-denied-million-from-slot/article_411d78f2-28a0-5e0a-bc16-73e8c79fc3b7.html|title=Woman sues Isle after she's denied $42 million from slot malfunction|author=Jeff Reinitz|work=Waterloo Cedar Falls Courier}}</ref> Two such cases occurred in casinos in Colorado in 2010, where [[Software bug|software errors]] led to indicated jackpots of $11 million and $42 million.<ref>[http://www.lotterypost.com/news/215240 $11 million slot jackpot a malfunction, casino says ''Lottery Post'' 4 June 2010  ]</ref> Analysis of machine records by the state Gaming Commission revealed faults, with the true jackpot being substantially smaller.<ref>[http://spectrum.ieee.org/riskfactor/computing/software/woman-who-thought-she-won-42-million-at-casino-gets-2018 Woman Who Thought She Won $42 Million At Casino Gets $20.18 Instead ''IEEE Spectrum'' 25 May 2010 ]</ref> State gaming laws do not require a casino to honour payouts.

==Regional variations==
[[Image:Las Vegas slot machines.jpg|right|thumb|Row of slot machines inside [[McCarran International Airport]] in Las Vegas]]

===United States===
In the United States, the public and private availability of slot machines is [[United States state slot machine ownership regulations|highly regulated by state governments]]. Many states have established [[gaming control board]]s to regulate the possession and use of slot machines.

[[Nevada]] is the only state that has no significant restrictions against slot machines both for public and private use. In [[New Jersey]], slot machines are only allowed in hotel casinos operated in [[Atlantic City, New Jersey|Atlantic City]]. Several states ([[Illinois]], [[Indiana]], [[Louisiana]] and [[Missouri]]) allow slot machines (as well as any casino-style gambling) only on licensed [[riverboat]]s or permanently anchored [[barge]]s. Since [[Hurricane Katrina]], [[Mississippi]] has removed the requirement that casinos on the Gulf Coast operate on barges and now allows them on land along the shoreline. [[Delaware]] allows slot machines at three horse tracks; they are regulated by the [[Delaware Lottery|state lottery]] commission. In Wisconsin, bars and taverns are allowed to have up to five machines. These machines usually allow a player to either take a payout, or gamble it on a double-or-nothing "side game". A player redeems his winnings by pressing a button to print a ticket, which the bartender redeems for cash.

The [[Unincorporated territories of the United States|territory]] of [[Puerto Rico]] places significant restrictions on slot machine ownership, but the law is widely flouted and slot machines are common in bars and coffeeshops.<ref>{{cite web|url=http://www.deseretnews.com/article/765596778/Illegal-slot-machines-threaten-Puerto-Rico-casinos.html?pg=all|publisher=[[Deseret News]]|last=Coto|first=Danica|date=August 13, 2012|title=Illegal slot machines threaten Puerto Rico casinos|accessdate=June 23, 2016}}</ref>

====Private ownership====
[[Alaska]], [[Arizona]], [[Arkansas]], [[Kentucky]], [[Maine]], [[Minnesota]], [[Nevada]], [[Ohio]], [[Rhode Island]], [[Texas]], [[Utah]], [[Virginia]], and [[West Virginia]] place no restrictions on private ownership of slot machines. Conversely, in [[Connecticut]], [[Hawaii]], [[Nebraska]], [[South Carolina]], and [[Tennessee]], private ownership of any slot machine is completely prohibited. The remaining states allow slot machines of a certain age (typically 25–30 years) or slot machines manufactured before a specific date. For a detailed list of state-by-state regulations on private slot machine ownership, see [[U.S. state slot machine ownership regulations]].

====Native American casinos====
[[Native Americans in the United States|Native American]] casinos located in [[Indian reservation|reservations]] are not permitted to have slot machines unless the tribe first reaches a pact with the state in which it is located (per [[Indian Gaming Regulatory Act]]). Typically, a pact entitles the state to receive a fraction of the gross revenue from slot machines.

====Slot machine classes====
Some states have restrictions on the type (called "class") of slot machines that can be used in a casino or other gaming area. "Class III" (or "traditional") slot machines operate independently from a [[centralized system|centralized computer system]] and a player's chance of winning any payout is the same with every play. Class III slot machines are most often seen in Nevada or Atlantic City and are sometimes referred to as "Vegas-style slots".

==Legislation==

===United States===
The Indian Gaming Regulatory Act establishes three classes of games with a different regulatory scheme for each:<ref>http://www.nigc.gov/Laws_Regulations/Indian_Gaming_Regulatory_Act.aspx#2703</ref>

====Three classes====

=====Class I=====
Class I gaming is defined as (1) traditional Indian gaming, which may be part of tribal ceremonies and celebrations, and (2) social gaming for minimal prizes. Regulatory authority over class I gaming is vested exclusively in tribal governments and is not subject to IGRA's requirements.<ref>Utter, Jack. ''American Indians: Answers to Today's Questions'', 2nd edition, University of Oklahoma Press, 2001 (362)</ref>

=====Class II=====
Class II gaming is defined as the game of chance commonly known as bingo (whether or not electronic, computer, or other technological aids are used in connection therewith) and, if played in the same location as the [[Bingo (US)|bingo]], pull tabs, punch board, tip jars, instant bingo, and other games similar to bingo. Class II gaming also includes non-banked [[card games]], that is, games that are played exclusively against other players rather than against the house or a player acting as a bank. The Act specifically excludes slot machines or electronic facsimiles of any game of chance from the definition of class II games.

Tribes retain their authority to conduct, license, and regulate class II gaming, provided it complies with the Act - including the requirement that the Tribal government adopt a gaming ordinance approved by the National Indian Gaming Commission (NIGC). Tribal governments are the primary entity responsible for regulating class II gaming on its lands. Only Hawaii and Utah continue to prohibit all types of gaming.
<ref>Indian Gaming Regulatory Act.  25 U.S.C. §2703(7)(A)(i)</ref>

=====Class III=====
The definition of class III gaming is broad. It includes all forms of gaming that are neither class I nor II. Games commonly played at [[casino]]s, such as [[slot machines]], [[blackjack]], [[craps]], and [[roulette]], clearly fall in the class III category, as well as wagering games and electronic facsimiles of any game of chance. Generally, class III is often referred to as casino-style gaming. As a compromise, the Act restricts Tribal authority to conduct class III gaming.

Before a Tribe may lawfully conduct class III gaming, the following conditions must be met: 
*The Particular form of class III gaming that the Tribe wants to conduct must be permitted in the state in which the tribe is located.
*The Tribe and the state must have negotiated a compact that has been approved by the Secretary of the Interior, or the Secretary must have approved regulatory procedures.
*The Tribe must have adopted a Tribal gaming ordinance that has been approved by the Chairman of the Commission.

The regulatory scheme for class III gaming is more complex than a casual reading of the statute might suggest. Although Congress clearly intended regulatory issues to be addressed in [[Tribal-State compacts]], it left a number of key functions in federal hands, including approval authority over compacts, management contracts, and Tribal gaming ordinances. Congress also vested the Commission with broad authority to issue regulations in furtherance of the purposes of the Act. Accordingly, the Commission plays a key role in the regulation of class II and III gaming.

====Slot clubs====
Many American casinos offer free memberships in "slot clubs", which return a fraction of the amount of money that is bet in the form of [[comps (casino)|comps]] (complimentary food, drinks, hotel rooms, or merchandise), or sometimes as cash or a promise to pay cash at a later date. These clubs require that players use cards that are inserted into the slot machines, to allow the casinos to track the players' "action" (how much each player bets and for how long), which is often used to establish levels of play that may make players eligible for additional comps.

===Canada===
The Government of Canada has minimal involvement in gambling beyond the Canadian [[Criminal Code (Canada)|Criminal Code]]. In essence the term “lottery scheme", used in the code, means slot machines, bingo and table games normally associated with a casino. These fall under the jurisdiction of the province or territory without reference to the federal government. Thus no two provincial regulatory or operational regimes are the same.

The 10 provinces all have gaming departments and slot machine play is available in venues across all. Part of the revenues go to the local government which in turn gives a percentage to the federal government. Choice of slots available is a province by province negotiation with the local Gaming Department. Individual territories have such small populations that there are no dedicated departments or land based facilities to play.

The history of First Nation's gaming in Canada is short but contentious. Only 12 First Nation casinos exist scattered over five provinces. The [[Assembly of First Nations]] view jurisdiction over gaming on First Nation land as part of their constitutional rights protected by section 35(1) of the [[Constitution Act, 1982]]. However the Supreme Court of Canada has rejected First Nation's claims to a right to conduct gaming activities. Nevertheless, the First Nation casino's largest revenue driver is from slot machine play and the regulation of these is by agreement with an Indigenous Gaming Regulator, a delegated sub-group of each province Gaming Authority.

All provinces have dedicated problem gambling help lines and research, and the territories have health and social service support for individuals with gambling problems.

===Australia===
In [[Australia]] "Poker Machines" or "pokies"<ref>{{cite web | url=http://australiannationaldictionary.com.au/index.php | title=Australian National Dictionary: Pokie | publisher=Oxford University Press | accessdate=2 October 2014}}</ref> are officially termed "gaming machines". Australian-style gaming machines frequently use video displays to simulate physical reels, usually five. These machines have additional bonusing and second-screen features such as free games and bonus levels. They also allow for multiple lines (up to 200) or multiple ways (up to 3,125) to be played. Late in 2010, there were 200,057 poker machines operating in Australia, which was 2.75% of the 7,249,919 gaming machines worldwide.<ref>{{cite web |url=http://www.tnsglobal.com/global/alm/australia/ |title=TNS |publisher=Tnsglobal.com |date= |accessdate=2012-08-14 |deadurl=yes |archiveurl=http://arquivo.pt/wayback/20080224070741/http%3A//www.tnsglobal.com/global/alm/australia/ |archivedate=2008-02-24 |df= }}</ref>

On multiway games, players play the entire position of each reel instead of fixed lines or patterns. For instance, if a player plays 1 reel on a 243 way game, they receive three symbols in the first reel which pay anywhere in the three positions, while all other reels pay in the centre only, with unused areas darkened. On the other end of the scale, if the player plays 5 reels, symbols can appear anywhere in the window and will pay as long as there is one in each reel. Most games however still require the symbols appearing left to right, sometimes this even includes scatters. Scatter symbols still pay the same as per conventional games, multiplying their pay amount by the total bet and the number of ways/reels played. Other multiway games give you even more ways by using a 4x5 or 5x5 pattern, where there are up to 5 symbols in each reel, allowing for up to 1,024 and 3,125 ways to win respectively. Aristocrat calls these games ''Xtra Reel Power'' and ''Super Reel Power'' respectively. These games typically cost more than their 243 way ''Reel Power'' counterparts. Recently, [[International Game Technology|IGT]] has also started to manufacture multiway games. Gaming machine manufacturer [[Konami|Konami Australia]] also made an alternative way of gaming by using patterns, where symbols pay adjacent to one another. Most of these games have a hexagonal reel formation, and much like multiway games, any patterns not played are darkened out of use. On both systems, scatter symbols still pay in the darkened areas just like standard machines where scatters don't have to appear on a payline.

The laws regulating the use of gaming machines in Australia are a matter for State governments, and as such they vary between States.

Gaming machines are found in casinos (approximately one in each major city) as well as [[pub]]s and clubs in some states (usually sports, social, or [[Returned and Services League of Australia|RSL]] clubs). The first Australian state to legalize this style of gambling was [[New South Wales]] in 1956 when they were made legal in all registered clubs in the state. There are suggestions that the proliferation of poker machines has led to increased levels of [[problem gambling]]; however, the precise nature of this link is still open to research.<ref>[http://www.pc.gov.au/inquiry/gambling/finalreport/index.html PC.gov.au] {{webarchive|url=https://web.archive.org/web/20060819030433/http://www.pc.gov.au/inquiry/gambling/finalreport/index.html |date=2006-08-19 }}, see Chapter 8, Productivity Commission Report no. 10</ref>

In 1999 the Australian Productivity Commission reported that nearly half Australia's gaming machines were in New South Wales. At the time, 21% of all the gambling machines in the world were operating in Australia, and on a per capita basis, Australia had roughly five times as many gaming machines as the United States. Australia ranks 8th in terms of the total number of gaming machines after Japan, USA, Italy, UK, Spain and Germany. The primary reason for this is that gaming machines have been legal in the state of New South Wales since 1956 and over that time the number of machines has grown to 97,103 (at December 2010, including the Australian Capital Territory). By way of comparison, the US State of Nevada which legalised gaming including slots several decades before NSW, had 190,135 slots operating.<ref>{{cite news|title=One pokie for every 110 of us|url=http://www.smh.com.au/national/one-pokie-for-every-110-of-us-20100116-mdf3.html|accessdate=28 November 2015|agency=SMH|publisher=Fairfax Media|date=17 January 2010}}</ref>

Revenue from gaming machines in pubs and clubs accounts for more than half of the $4 billion in gambling revenue collected by state governments in fiscal year 2002&nbsp;&ndash; 03 <ref>[http://www.unoslots.com/ageing.pdf Productivity Commission, Economic Implications of an Ageing Australia, April 12, 2005, Technical Paper No.10, "Gambling revenue"]</ref>

In [[Queensland]], gaming machines in pubs and clubs must provide a return rate of 85% while machines located in casinos must provide a return rate of 90%.<ref>{{cite web|url=http://www.onlinepokiespro.net/australians-bet-others|title=Australians bet more than others|date=7 April 2015|work=Online Pokies Pro}}</ref> Most other states have similar provisions. In [[Victoria, Australia|Victoria]], gaming machines must provide a minimum return rate of 87% (including jackpot contribution), including machines in [[Crown Melbourne|Crown Casino]]. As of December 1, 2007, all gaming machines with support for $100 notes were banned due to an amendment to the gaming laws; all gaming machines made since 2003 comply with this rule. This new law also banned machines which would automatically play with the button held. One exception to these laws exists in Crown Casino, any player with a VIP loyalty card can still insert $100 notes and use the autoplay feature, whereby the machine will continue to play without player intervention until credit is exhausted or the player intervenes. All gaming machines in Victoria have an information screen accessible to the user by pressing the 'i key' button, showing the game rules, paytable, return to player percentage, and the top and bottom five combinations, with the odds shown. These combinations are stated to be played on a minimum bet (usually 1 credit per line, with 1 line or reel played), excluding feature wins.

[[Western Australia]] only permits the use of particular forms of gaming machine in [[Burswood Entertainment Complex|Burswood casino]], and no gaming machines may be used elsewhere. This policy (the most restrictive in Australia) had a long historical basis, and was reaffirmed by the 1974 Royal Commission into Gambling:

<blockquote>...poker machine playing is a mindless, repetitive and insidious form of gambling which has many undesirable features. It requires no thought, no skill or social contact. The odds are never about winning. Watching people playing the machines over long periods of time, the impressionistic evidence at least is that they are addictive to many people. Historically poker machines have been banned from Western Australia and we consider that, in the public interest, they should stay banned. –Report of the Royal Commission into Gambling 1974, p. 72
</blockquote>
[[Nick Xenophon]] was elected on an independent [[No Pokies]] ticket in the [[South Australian Legislative Council]] at the [[South Australian state election, 1997|1997 South Australian state election]] on 2.9 percent, and re-elected at the [[South Australian state election, 2006|2006 election]] on 20.5 percent, before being elected to the [[Australian Senate]] at the [[Australian federal election, 2007|2007 federal election]] on 14.8 percent. Independent candidate [[Andrew Wilkie]], an anti-pokies campaigner, was elected to the [[Australian House of Representatives]] seat of [[Division of Denison|Denison]] at the [[Australian federal election, 2010|2010 federal election]]. Wilkie was one of four crossbenchers who supported the [[Julia Gillard|Gillard]] [[Australian Labor Party|Labor]] government following the [[hung parliament]] result. Wilkie immediately began forging ties with Xenophon as soon as it was apparent that he was elected. In exchange for Wilkie's support, the Labor government are attempting to implement pre-commitment technology for high-bet/high-intensity poker machines, against opposition from the [[Tony Abbott]] [[Coalition (Australia)|Coalition]] and Clubs Australia.

=== Russia ===
In Russia, slot clubs appeared quite late, only in 1992. Before 1992 slot machines were only in the casino and in small shops, but later slot clubs began to grow over the country. The most popular and numerous clubs were "Vulcan 777" and "Taj Mahal". After 2009, when a ban on gambling establishments, almost all slot clubs disappeared, and appeared only in a specially authorized gambling zones.

===United Kingdom=== <!-- [[Fixed odds betting terminal]] links here. -->
[[Image:Old fruit machines in Teignmouth 10-08-06.jpg|thumb|right|Row of old fruit machines in Teignmouth Pier, Devon]]
[[Image:Slot machines at Wookey Hole Caves.JPG|thumb|right|One armed bandits at [[Wookey Hole Caves]]]]
The provision of slot machines is covered by the [[Gambling Act 2005]]. This superseded the [[Gaming Act 1968]].<ref name=GamingAct>{{cite web|url=http://www.opsi.gov.uk/si/si2005/20052776.htm|title=Gaming Act 2005|year=2005|publisher=[[The Stationery Office]]|accessdate=2 November 2009}}</ref>

Slot machines in the UK are categorised by definitions produced by the [[Gambling Commission]] as part of the legislation brought in with the Gambling Act of 2005.

{| class="wikitable"
|-
! Machine category
! Maximum stake (from January 2014)
! Maximum prize (from January 2014)
|-
|A
|Unlimited
|Unlimited
|-
|B1
|£5
|£10,000 or if the game has a progressive jackpot that can be £20,000
|-
|B2
|£100 (in multiples of £10)
|£500
|-
|B3
|£2
|£500
|-
|B3A
|£1
|£500
|-
|B4
|£2
|£400
|-
|C
|£1
|£100 or £200 If jackpot is repeated
|-
|D (various)
|10p to £8
|£8 cash or £50 non-cash
|}

Casinos built under the provisions of the 1968 Act are allowed to house up to twenty machines categories B to D or any number of C or D machines instead. As defined by the 2005 Act, large casinos will have a maximum of one hundred and fifty machines of any combination of machines in categories B to D, within the total limit of one hundred and fifty (subject to machine to table ratio of 5:1) and small casinos will have a maximum of eighty machines of any combination of machines in categories B to D, within the total limit of eighty (subject to machine to table ratio of 2:1).

====Category A====
Category A games were defined in preparation for the planned "[[Regional casino|Super Casinos]]." Despite a lengthy bidding process, with [[Manchester]] being chosen as the single planned location, the development was cancelled soon after [[Gordon Brown]] became [[Prime Minister of the United Kingdom]]. As a result, there are no lawful Category A games in the UK.

====Category B====
Category B games are divided into subcategories. However, the differences between B1, B3 and B4 games are mainly the stake and prizes as defined in the above table. Category B2 games &ndash; [[Fixed odds betting terminal]]s (FOBTs) &ndash; have quite different stake and prize rules. FOBTs are mainly found in licensed [[betting shop]]s, or bookmakers, usually in the form of electronic [[roulette]].

The games are based on a [[random number generation|random number generator]] and thus the probability of getting the jackpot in each game is independent of any other game, and these probabilities are all equal. If a [[pseudorandom number generator]] is used instead of one that is truly random, the probabilities are not truly independent, since each pseudorandom number is determined at least in part by the one generated before it.

====Category C====
Category C games are often referred to as '''fruit machines''', '''one-armed bandits''' and '''AWP''' ([[Amusement With Prizes]]). Fruit machines are commonly found in [[public house|pubs]], [[Nightclub|club]]s, and [[video arcade|arcade]]s. Machines commonly have three reels, but can be found with four or five reels with around sixteen to twenty-four symbols printed around them. The reels are spun each play, and if certain combinations of symbols appear then winnings are paid by the machine, or a subgame is played. These games often have many extra features, trails and subgames with opportunities to win money; usually more than can be won from just the payouts on the reel combinations.

Fruit machines in the UK almost universally have the following features, generally selected at random using a [[pseudorandom number generator]]:
* A player (known in the industry as a ''punter'') may be given the opportunity to ''hold'' one or more reels before spinning, meaning that the reel will not be spun at the next play, but will instead retain its setting at the previous spin. This can sometimes increase the chance of winning, especially if two or more reels are held.
* A player may also be given a number of ''nudges'' following a spin (or, in some machines, as a result in a subgame). A nudge is a single step rotation of a reel of the player's choice (although the machine may not allow all reels to be nudged for a particular play).
* ''Cheats'' can also be made available on the internet or through emailed newsletters for subscribers. These cheats give the player the impression of an advantage, whereas in reality the payout percentage remains exactly the same. The most widely used cheat is known as '''Hold after a nudge''' and increases the chance that the player will win following an unsuccessful nudge. The cheats give the player an incentive to play the latest games.{{Citation needed|date=November 2009}} In reality whilst machines from the early 1990s did not advertise the concept of '''Hold after a nudge''' when this feature was first introduced, it became so well known amongst players and widespread amongst new machine releases that it is now well advertised on the machine during play. This is characterized by messages on the display such as ''DON'T HOLD ANY'' or ''LET 'EM SPIN'' and is a designed feature of the machine, not a cheat at all.

It is known for machines to pay out multiple jackpots, one after the other (this is known as a '''streak''' or '''rave''') but each jackpot requires a new game to be played so as not to violate the law about the maximum payout on a single play. Typically this involves the player only pressing the Start button for which a single credit is taken, regardless of whether this causes the reels to spin or not. The minimum payout percentage is 70%, with pubs often setting the payout at around 78%.

===Japan===
[[Japan]]ese slot machines, known as {{nihongo|'''pachisuro'''|[[:ja:パチスロ|パチスロ]]}} or '''pachislot''' ([[portmanteau]]s of the words "pachinko" and "slot machine"), are a descendant of the traditional Japanese [[pachinko]] game. Slot machines are a fairly new phenomenon and they can be found in mostly in pachinko parlors and the adult sections of [[Video arcade|amusement arcade]]s, known as game centers.

The machines are regulated with [[integrated circuit]]s, and have six different levels changing the odds of a [[777 (number)#Gambling and luck|777]]. The levels provide a rough outcome of between 90% to 160% (200% for skilled players). Indeed, Japanese slot machines are "beatable." Parlor operators naturally set most machines to simply collect money, but intentionally place a few paying machines on the floor so that there will be at least someone winning,{{Citation needed|date=February 2007}} encouraging players on the losing machines to keep gambling, using the psychology of the [[gambler's fallacy]].

Despite the many varieties of pachislot machines, there are certain rules and regulations put forward by the {{nihongo|"Security Electronics and Communication Technology Association"|[[:ja:保安電子通信技術協会|保安電子通信技術協会]]}}, an affiliate of the [[National Police Agency (Japan)|National Police Agency]]. For example, there must be three reels. All reels must be accompanied by buttons which allow players to manually stop them, reels may not spin faster than 80 RPM, and reels must stop within 0.19 seconds of a button press. In practice, this means that machines cannot let reels slip more than 4 symbols. Other rules include a 15 coin payout cap, a 50 credit cap on machines, a 3 coin maximum bet, and other such regulations.{{Citation needed|date=February 2007}}

Although a 15 coin payout may seem quite low, regulations allow "Big Bonus" (~400–711 coins) and "Regular Bonus" modes (~110 coins) where these 15 coin payouts occur nearly continuously until the bonus mode is finished. While the machine is in bonus mode,  the player is entertained with special winning scenes on the LCD display, and energizing music is heard, payout after payout.

Three other unique features of Pachisuro machines are "Stock", "Renchan", and {{Nihongo|''tenjō''|天井}}. On many machines, when enough money to afford a bonus is taken in, the bonus is not immediately awarded. Typically the game merely stops making the reels slip off the bonus symbols for a few games. If the player fails to hit the bonus during these "standby games", it is added to the "Stock" for later collection. Many current games, after finishing a bonus round, set the probability to release additional stock (gained from earlier players failing to get a bonus last time the machine stopped making the reels slip for a bit) very high for the first few games. As a result, a lucky player may get to play several bonus rounds in a row (a "Renchan"), making payouts of 5,000 or even 10,000 coins possible. The lure of "Stock" waiting in the machine, and the possibility of "Renchan" tease the gambler to keep feeding the machine. To tease him further, there is a ''tenjō'' (ceiling), a maximum limit on the number of games between "Stock" release. For example, if the ''tenjō'' is 1,500, and the number of games played since the last bonus is 1,490, the player is guaranteed to release a bonus within just 10 games.

Because of the "Stock", "Renchan", and ''tenjō'' systems, it is possible to make money by simply playing machines on which someone has just lost a huge amount of money. This is called being a "[[hyena]]". They are easy to recognize, roaming the aisles for a "Kamo" ("[[Gullibility|sucker]]" in English) to leave his machine.

In short, the regulations allowing "Stock", "Renchan", and ''tenjō'' transformed the Pachisuro from a low-stakes form of entertainment just a few years back to hardcore gambling. [[Problem gambling|Many people may be gambling more than they can afford]], and the big payouts also lure unsavory "hyena" types into the gambling halls.

To address these social issues, a new regulation (Version 5.0) was adopted in 2006 which caps the maximum amount of "stock" a machine can hold to around 2,000–3,000 coins' worth of bonus games. Moreover, all Pachisuro machines must be re-evaluated for regulation compliance every three years. Version 4.0 came out in 2004, so that means all those machines with the up to 10,000 coin payouts will be removed from service by 2007. Only time will tell how these changes will affect the Japanese Pachisuro industry.

==Problem gambling and slot machines==
Natasha Dow Schüll, associate professor in the Program in Science, Technology, and Society at the Massachusetts Institute of Technology<ref>{{cite web|url=http://www.natashadowschull.org|title=Natasha Dow Schull academic website Science, Technology, and Society MIT|work=natashadowschull.org}}</ref> uses the term “machine zone” to describe the sensation which the users of slot machine experience during gambling, where is a distortion in the perception of time, related to a system of sound and visual rewards.<ref>http://press.princeton.edu/chapters/i9156.pdf</ref>

Mike Dixon, PhD, professor of psychology, University of Waterloo, Ontario, Canada<ref>{{cite web|url=https://uwaterloo.ca/psychology/people-profiles/mike-j-dixon|title=Mike J. Dixon|work=Psychology}}</ref> studies the relationship between slot players and slot machines. Slot players were observed experiencing heightened arousal from the [[Stimulus (physiology)|sensory stimulus]] coming from the machines. They "sought to show that these "losses disguised as wins" (LDWs) would be as arousing as wins, and more arousing than regular losses".<ref>{{cite web|url=http://www.dailymail.co.uk/news/article-2357161/How-music-sound-slot-machines-convinces-you-winning.html#ixzz3IJ6pMBA0|title=How music and sound of slot machines convinces you you¿re winning|date=5 July 2013|work=Mail Online}}</ref>

[[File:Mills Novelty Co. Horse Head Bonus Antique Slot Machine.jpg|thumb|Mills Novelty Co. Horse Head Bonus antique slot machine]]

==Skill stops==
Skill stop buttons predated the Bally electromechanical slot machines of the 1960s and 70s. They appeared on mechanical slot machines manufactured by Mills Novelty Co. as early as the mid 1920s. These machines had modified reel-stop arms, which allowed them to be released from the timing bar, earlier than in a normal play, simply by pressing the buttons on the front of the machine, located between each reel.

"Skill stop" buttons were added to some slot machines by Zacharias Anthony in the early 1970s. These enabled the player to stop each reel, allowing a degree of "skill" so as to satisfy the [[New Jersey]] gaming laws of the day which required that players were able to control the game in some way. The original conversion was applied to approximately 50 late model Bally slot machines. Because the typical machine stopped the reels automatically in less than 10 seconds, weights were added to the mechanical timers to prolong the automatic stopping of the reels. By the time the New Jersey Alcoholic Beverages Commission (ABC) had approved the conversion for use in New Jersey arcades the word was out and every other distributor began adding skill stops. The machines were a huge hit on the [[Jersey Shore]] and the remaining unconverted Bally machines were destroyed as they had become instantly obsolete.{{Citation needed|date=March 2008}}

==In literature==
Slot machines are discussed in the 2017 novel <i>Never Split Tens</i> by [[Les Golden]] of Oak Park, Illinois, published by Springer Nature.

==See also==
*[[Casino]]
*[[EUROMAT|European Gaming & Amusement Federation]]
*[[List of probability topics]]
*[[Pachinko]]
*[[Progressive jackpot]]
*[[Quiz machine]]
*[[United States state slot machine ownership regulations]]
*[[Video Lottery Terminal]]
*[[Video poker]]
*[[Problem gambling]]
*[[Video bingo]]

==References==
{{refs}}

==Bibliography==
*Brisman, Andrew. ''The American Mensa Guide to Casino Gambling: Winning Ways'' (Stirling, 1999) ISBN 0-8069-4837-X
*Grochowski, John. ''The Slot Machine Answer Book: How They Work, How They've Changed, and How to Overcome the House Advantage'' (Bonus Books, 2005)  ISBN 1-56625-235-0
*Legato, Frank. ''How to Win Millions Playing Slot Machines! ...Or Lose Trying'' (Bonus Books, 2004) ISBN 1-56625-216-4
{{Wikidata|Q33972}}
[[Category:American inventions]]
[[Category:Slot machines| ]]
[[Category:Arcade games]]
[[Category:Gaming devices]]
[[Category:Commercial machines]]