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[[Image:Blackjack board.JPG|thumb|300px|A blackjack game in progress]]

'''Card counting''' is a [[card game]] strategy used in [[blackjack]] to determine whether the next hand provides a probable advantage to the player.  The various systems developed provide a guide to strategy decision as well as the size of bets.  Card counting allows players to bet more with less risk when the deck is favorable. 

== Basics ==
The most common variations of card counting are based on theoretical and statistical evidence that high cards (especially aces and 10s) benefit the player more than the dealer, while the low cards, (especially 4s, 5s, and 6s) help the dealer while hurting the player. A high concentration of aces and 10s in the deck increases the player's chances of hitting a natural Blackjack, which pays out 3:2 (unless the dealer also has blackjack). Also, when the [[Shoe (cards)|shoe]] has a high concentration of 10s, players have a better chance of winning when doubling.<ref name="beat-1966">Thorp (1966), pp.24-27, pp. 41-47, pp. 98-99, pp. 102-103, p. 110, p. 115.</ref><!-- A high number of ten-value cards also makes the insurance bet more profitable since that is essentially a bet that the dealer's card is a ten (resulting in a dealer blackjack).--> Low cards benefit the dealer, since according to blackjack rules the dealer must hit ''stiff hands'' (12-16 total) while the player has the option to hit or stand. Thus a dealer holding (12-16) will bust every time if the next card drawn is a 10, making this card essential to track when card counting.<ref name="wiz-bjk">{{cite web |url=http://wizardofodds.com/blackjack |title=How to Play Blackjack |accessdate=2011-11-03 |publisher=wizardofodds.com |author=Wizard of Odds |year=2011 |month=July}}</ref>

Contrary to the popular myth, card counters do not need unusual mental abilities in order to count cards, because they are not tracking and memorizing specific cards. Instead, card counters assign a point score to each card they see that estimates the value of that card, and then they track the sum of these values &ndash; a process called keeping a "running count."<ref name="tob-1979">Griffin (1988)</ref> The myth that counters keep track of every card was portrayed in the movie ''[[Rain Man]]'', in which the [[Savant syndrome|savant]] character [[Raymond Babbitt]] counts through six decks with ease and a casino employee erroneously comments that it is impossible to count six decks.

=== Systems ===

Basic card counting assigns a positive, negative, or zero value to each card value available. When a card of that value is dealt, the count is adjusted by that card's counting value. Low cards increase the count as they increase the percentage of high cards in the remaining shoe, while high cards decrease it for the opposite reason. For instance, the Hi-Lo system subtracts one for each dealt ten, Jack, Queen, King or Ace, and adds one for any value 2-6. Values 7-9 are assigned a value of zero and therefore do not affect the count.<ref>Axelrad (2010), p. 256.</ref>

The goal of a card counting system is to assign point values that roughly correlate to a card's Effect of Removal (EOR). The EOR is the actual effect of removing a given card from play, and the resulting impact on the house advantage. The player may gauge the effect of removal for all cards dealt, and assess the current house advantage of a game based on the remaining cards.  As larger ratios between point values are used to create better correlation to actual EOR with the goal of increasing the efficiency of a system, such systems use larger and larger numbers and are broken into classes such as level 1, level 2, level 3, and so on, with regards to the ratio between the highest and lowest assigned point values.

The High-Low system is considered a ''single-level'' or ''level-one'' count, because the count never increases or decreases by more than a single, predetermined value. A ''multilevel'' count, such as Zen Count or Wong Halves, makes finer distinctions between card values to gain greater play accuracy. Rather than all cards having a value of +1, 0, or −1, an advanced count might also include card ranks that are counted as +2 and −2, or +0.5. Advanced players might additionally maintain a ''side count'' (separate count) of specific cards, such as a side count Aces, to deal with situations where the best count for betting accuracy differs from the best count for playing accuracy.

The disadvantage of higher-level counts is that keeping track of more information can detract from the ability to play quickly and accurately. A card-counter might earn more money by playing a simple count quickly—more hands per hour played—than by playing a complex count slowly.

Since the 1960’s numerous computer-based systems have been developed.  The following table summarizes the values assigned to the cards in the most popular and most powerful systems. References are provided to the published books of computer analyst experts, most holding advanced degrees including the Ph.D or M.A. in mathematics or probability and statistics, who developed the systems.  Only authors of reputable, published books, in which the systems have been published, as opposed to any of the hundreds of self-published commercial websites, are referenced.  The card value assignments of a comprehensive list of one hundred possible systems, up to level four systems, are provided by [[Blackjack Hall of Fame]] member [[Arnold Snyder]].<ref> http://www.blackjackforumonline.com/content/hundred.htm </ref>  


{| class="wikitable" border="1"
|- style="text-align:center;"
!style="background:#B0C4DE"|System Name
!style="background:#B0C4DE"|2s
!style="background:#B0C4DE"|3s
!style="background:#B0C4DE"|4s
!style="background:#B0C4DE"|5s
!style="background:#B0C4DE"|6s
!style="background:#B0C4DE"|7s
!style="background:#B0C4DE"|8s
!style="background:#B0C4DE"|9s
!style="background:#B0C4DE"|10s
!style="background:#B0C4DE"|A’s
!style="background:#B0C4DE"|Developer
|-
|Advanced Omega II<ref>Carlson, Bryce  (2010) ''Blackjack for Blood'', Gamestar Pr Inc</ref>    
|1
|1
|2
|2
|2
|1
|0 
| -1
| -2
|0
|Bryce Carlson
|-
|Canfield Expert<ref name="Canfield">{{cite web|url= http://books.google.com/books/about/Blackjack_your_way_to_riches.html?id=6tXtee819p0C |title= Canfield Expert book |publisher= |date= |accessdate=2012-11-24}}</ref>     
|0 
|1
|1
|1
|1
|1
|0 
| -1
| -1
|0
|Richard Canfield (John Hinton)
|-
|Canfield Master<ref name="Canfield"/>
|1
|1
|2
|2
|2
|1
|0 
| -1
| -2
|0
|Richard Canfield (John Hinton)
|-
|Complete Point Count or High-Low<ref>Thorp, Edward O.(1962) ''Beat the Dealer: A Winning Strategy for the Game of Twenty-One'', Vintage, New York</ref><ref name=''beat-1966''>Thorp, Edward O.(1966) ''Beat the Dealer: A Winning Strategy for the Game of Twenty-One'', revised edition, Vintage, New York.  Although ascribed to Thorp, the system was introduced by mathematician Dr. [[Harvey Dubner]].  The results published by Thorp were programmed by computer analyst Dr. Julian Braun</ref>
|1
|1
|1
|1
|1
|0 
|0 
|0 
| -1
| -1
|[[Edward O. Thorp]]
|-
|Hi-Opt I (High Optimum)<ref name="Humble">Humble, Lance and Cooper, Carl  (1987) ''The Worlds Greatest Blackjack Book '', Doubleday, New York</ref>
|0 
|1
|1
|1
|1
|0 
|0 
|0 
| -1
|0
|Lance Humble and Carl Cooper
|-
|Hi-Opt II (High Optimum)<ref name="Humble"/>
|1
|1
|2
|2
|1
|1
|0 
|0 
| -2
|0
|Lance Humble and Carl Cooper
|-
| Keep It Simple 2 (KISS 2)<ref>Renzey, Fred  (2006) ''Blackjack Bluebook '', Blackjack Mentor Press</ref>   
|1
|1
|1
|1
|1
|0 
|0 
|0 
| -1
|0
|Fred Renzey
|-
| Keep It Simple 3 (KISS 3)<ref>Renzey, Fred  (2006) ''Blackjack Bluebook II '', Blackjack Mentor Press</ref>     
| 0/1
|1
|1
|1
|1
|1
|0 
|0 
| -1
| -1
|Fred Renzey
|-
|Knock Out (K-O; All Sevens)<ref>Vancura, Olaf and Fuchs, Ken  (1998) ''Knock-Out Blackjack'', Huntington Press</ref><ref name=''british''>Zadehkoochak, M. (1992) ''The Book of British Blackjack'' Medimage. ISBN 1-897728-00-X</ref><ref>Notes:  The KO Strategy was first introduced in 1992 as the "All Sevens" count in ''The Book of British Blackjack''</ref>    
|1
|1
|1
|1
|1
|1
|0 
|0 
| -1
| -1
|Olaf Vancura and Ken Fuchs
|-
|Mentor<ref>Renzey, Fred  (2006) ''Blackjack Bluebook II '', Blackjack Mentor Press</ref>     
|1
|2
|2
|2
|2
|1
|0 
| -1
| -2
| -1
| Fred Renzey
|-
|Red Seven<ref>Snyder, Arnold  (1983) ''Blackbelt in Blackjack''</ref>     
|1
|1
|1
|1
|1
| 0/1
|0 
|0 
| -1
| -1
|[[Arnold Snyder]]
|-
|Revere 14 Count<ref name="Revere">Revere, Lawrence  (1971) ''Playing Blackjack as a Business '', Carol Publishing Group-Lyle Stuart</ref>
|2
|2
|3
|4
|2
|1
|0 
| -2
| -3
|0
|[[Lawrence Revere]] (G. Owens)
|-
|Revere Advanced Point Count (RAPC) <ref name="Revere"/>
|2
|3
|3
|4
|3
|2
|0 
| -1
| -3
| -4
|[[Lawrence Revere]] (G. Owens)
|-
|Revere Plus-Minus <ref name="Revere"/>
|1
|1
|1
|1
|1
|0
|0 
| -1
| -1
|0
|[[Lawrence Revere]] (G. Owens)
|-
|Revere Point Count (RPC) <ref name="Revere"/>
|1
|2
|2
|2
|2
|1
|0 
| -1 
| -2
| -2
|[[Lawrence Revere]] (G. Owens)
|-
|Silver Fox<ref>Stricker, Ralph, ''Silver Fox Blackjack System'', Gambler’s Book Club, Las Vegas</ref>    
|1
|1
|1
|1
|1
|1
|0 
| -1
| -1
| -1
|Ralph Stricker
|-
|Unbalanced Zen II (UBZ2)<ref> C., George, ''The Unbalanced Zen II'' in Schlesinger, Don (2008 ) ''Blackjack Attack:  Playing the Pros’ Way'', RGE Publishers</ref>     
|1
|2
|2
|2
|2
|1
|0 
|0 
| -2
| -1
|George C.
|-
|Uston Advanced Plus/Minus (APM)<ref name="Uston">Uston, Ken  (1998) ''Million Dollar Blackjack'', Carol Publishing Group</ref>
|0
|1
|1
|1
|1
|1
|0 
|0 
| -1
| -1
|[[Ken Uston]]
|-
|Uston Advanced Point Count (APC)<ref name="Uston"/>
|1
|2
|2
|3
|2
|2
|1
| -1
| -3
|0
|[[Ken Uston]]
|-
|Uston Strongest and Simplest (SS)<ref name="Uston"/>
|2
|2
|2
|3
|2
|1
|0 
| -1
| -2
| -2
|[[Ken Uston]]
|-
|Wong Halves<ref>Wong, Stanford  (1994) ''Professional Blackjack'', Pi Yee Pr Press</ref>     
|.5
|1
|1
|1.5
|1
|.5
|0 
| -.5
| -1
| -1
|[[Stanford Wong]] (John Ferguson)
|-
|Zen Count<ref>Synder, Arnold  (2005) ''Blackbelt in Blackjack'', Cardoza, Las Vegas</ref>     
|1
|1
|2
|2
|2
|1
|0 
|0 
| -2
| -1
|[[Arnold Snyder]]
|-
|}


===Design and selection of systems===

The primary goal of a card counting system is to assign point values to each card that roughly correlate to the card's "effect of removal" or EOR (that is, the effect a single card has on the house advantage once removed from play), thus enabling the player to gauge the house advantage based on the composition of cards still to be dealt. Larger ratios between point values can better correlate to actual EOR, but add complexity to the system. Counting systems may be referred to as "level 1", "level 2", etc., corresponding to the number of different point values the system calls for.

The ideal system is a system that is usable by the player and offers the highest average dollar return per period of time when dealt at a fixed rate. With this in mind, systems aim to achieve a balance of efficiency in three categories:

;Betting correlation (BC)
:When the sum of all the permutations of the undealt cards offer a positive expectation to a player using optimum playing strategy, there is a positive expectation to a player placing a bet. A system's BC gauges how effective a system is at informing the user of this situation.
;Playing efficiency (PE)
:A portion of the expected profit comes from modifying playing strategy based on the known altered composition of cards. For this reason, a system's PE gauges how effectively it informs the player to modify strategy according to the actual composition of undealt cards. A system's PE is important when the effect of PE has a large impact on total gain, as in single- and double-deck games.
;Insurance correlation (IC)
:A portion of expected gain from counting cards comes from taking the insurance bet, which becomes profitable at high counts. An increase in IC will offer additional value to a card counting system.

The observation of the ace plays a key role in such a way that when the ace has a distinct point value, you will see an increase in betting correlation since the ace is the most valuable card in the deck.  However alerting the player to the presence of additional aces in a deck decreases the efficiency of altering play decisions based on the count lowering a system's PE since the ace offers very little value when playing out a hand.  If a system does not assign a point value to an ace, it will see a decrease in BC with an increase in PE; in a situation in which the change in PE will offer a greater gain than a slight loss of BC, such a system is preferable.

One way to deal with such tradeoffs is to ignore the ace to yield higher PE while keeping a side count which is used to detect addition change in EV which the player will use to detect additional betting opportunities which ordinarily would not be indicated by the primary card counting system.

It is most common to keep a side count of aces since it is the most important card in terms of achieving a balance of BC and PE. In theory a player could keep a side count of every card and achieve a near 100% PE, however methods involving additional side counts for PE become more complex at an exponential rate as you add more side counts and the ability of the human mind is quickly overtasked and unable to make the necessary computations.

Since there is the potential to create an overtaxing demand on the human mind while using a card counting system another important design consideration is the ease of use.  Higher level systems, and systems with side counts will obviously become more difficult and in an attempt to make them easier, unbalanced systems eliminate the need for a player to keep tabs on the number of cards/deck that have already entered play typically at the expense of lowering PE.

===Golden Diagram===
After the publication of [[Beat the Dealer]] by Thorp, gambling casinos reacted to the advantage that a card counter  gains over the house by adopting counter strategies.  These included employing multiple decks rather than the single hand-held deck.  Two-deck games and games employing four and six decks dealt from a so-called shoe became commonplace.

Players soon realized intuitively that both these changes in the game reduced their probabilities of winning.  In games with a multiple deck, compared to single-deck or double-deck games, players experience frequency, magnitude, and depth (the fraction of the deck which has been dealt in playing previous hands) effects:  1) The deck becomes favorable less frequently at all depths, 2) when the deck does becomes favorable, the magnitude of the advantage is not as great, 3) all decks are favorable infrequently until a significant portion of the deck has been dealt and this occurs at greater depths into the deck in games  using multiple decks.

Blackjack professional and writer [[Les Golden]], based on a [[Monte Carlo simulation]] and theoretical arguments, calculated the magnitude of these effects.  The results of his analysis are displayed as Golden diagrams.<ref>Golden, Les (2010).   “Countering the Casino Countering of Counters:  The Golden Diagram to the Rescue,” ''Bluff Europe'',  June, p. 84-85</ref><ref>Golden, Les (2011). “Trust Me:  An Undetectable Winning System For Blackjack! ,” ''Bluff Europe'', March, p. 94-95</ref>  He also suggested a stepwise betting strategy to reduce the effects.<ref>Golden, Leslie M. (2011). “An Analysis of the Disadvantage to Players of Multiple Decks in the Game of 21.”  ''The Mathematical Scientist'', '''32''', 2,  p. 57-69</ref><ref>Golden, Les (2011). “Stepping Out With My Baby:  The Stepwise Betting Strategy,” ''Bluff Europe'', April, p. 92-93</ref>

== Running counts versus true counts in balanced counting systems ==

The Running count is the running total of each card's assigned value. When using balanced count (such as the High-Low or Hi-Lo system), the Running count is converted into a "True count," which takes into consideration the number of decks used. With Hi-Lo, the True count is essentially the Running count divided by the number of decks that haven't yet been dealt; this can be calculated exactly or approximated with an average card count per round times the number of rounds dealt.  Variations exist.

== Back-counting ==

Back-counting, also known as "Wonging," consists of standing behind a blackjack table that other players are playing on, and counting the cards as they are dealt.  [[Edward O. Thorp]] originally proposed the concept as “striking when the deck gets hots” in Beat The Dealer.

The player will enter or "Wong in" to the game when the count reaches a point at which the player has an advantage. The player may then raise his/her bets as their advantage increases, or lower their bets as their advantage goes down. Some back-counters prefer to flat-bet, and only bet the same amount once they have entered the game. Some players will stay at the table until the game is shuffled, or they may "Wong out" or leave when the count reaches a level at which they no longer have an advantage.

Back-counting is generally done on shoe games, of 4, 6, or 8 decks, although it can be done on pitch games of 1 or 2 decks. The reason for this is that the count is more stable in a shoe game, so a player will be less likely to sit down for one or two hands and then have to get up. In addition, many casinos do not allow "mid-shoe entry" in single or double deck games which makes Wonging impossible. Another reason is that many casinos exhibit more effort to thwart card counters on their pitch games than on their shoe games, as a counter has a smaller advantage on an average shoe game than in a pitch game.<ref>{{cite web|url=http://www.blackjackforumonline.com/content/6DeckText.htm |title=How to Use Frequency Distributions to Determine Your Card Counting Win Rate and Fluctuations |publisher=Blackjackforumonline.com |date= |accessdate=2009-03-20}}</ref>

=== Advantages ===

Back-counting is different from traditional card-counting, in that the player does not play every hand he sees. This offers several advantages. For one, the player does not play hands at which he does not have a statistical advantage. This in turn reduces variance and fluctuations, and increases the total advantage of the player. Another advantage is that the player does not have to change their bet size as much, or at all if they choose. Large variations in bet size are one way that casinos detect card counters, and this is eliminated with back-counting.

=== Disadvantages ===

There are several disadvantages to back-counting. One is that the player frequently does not stay at the table long enough to earn [[Comps (casino)|comps]] from the casino. Another disadvantage is that some players may become irritated with players who enter in the middle of a game, and superstitiously believe that this interrupts the "flow" of the cards. Lastly, a player who hops in and out of games may attract unwanted attention from casino personnel, and may be detected as a card-counter.

=== Group counting ===

While a single player can maintain their own advantage with back-counting, card counting is most often used by teams of players to maximize their advantage. In such a team, some players called "spotters" will sit at a table and play the game at the table minimum, while keeping a count (basically doing the back "counting"). When the count is significantly high, the spotter will discreetly signal another player, known as a "big player," that the count is high (the table is "hot"). The big player will then "Wong in" and wager vastly higher sums (up to the table maximum) while the count is high. When the count "cools off" or the shoe is shuffled (resetting the count), the big player will "Wong out" and look for other counters who are signaling a high count. This was the system used by the [[MIT Blackjack Team]], whose story was in turn the inspiration for the Canadian movie ''[[The Last Casino]]'' which was later re-made into the [[Cinema of the United States|Hollywood]] version ''[[21 (2008 film)|21]]''.<ref>Axelrad (2010), pp. 19, 259.</ref>

The main advantage of group play is that the team can count several tables while a single back-counting player can usually only track one table. This allows big players to move from table to table, maintaining the high-count advantage without being out of action very long. It also allows redundancy while the big player is seated as both the counter and big player can keep the count (as in the movie ''21'', the spotter can communicate the count to the big player discreetly as he/she sits down). The disadvantages include requiring multiple spotters who can keep an accurate count, splitting the "take" among all members of the team, requiring spotters to play a table regardless of the count (using only basic strategy, these players will lose money long-term), and requiring signals, which can alert pit bosses.

A simple variation removes the loss of having spotters play; the spotters simply watch the table instead of playing and signal big players to wong in as normal. The disadvantages of this variation are reduced ability of the spotter and big player to communicate, reduced comps as the spotters aren't sitting down, and vastly increased suspicion, as blackjack is not generally considered a spectator sport in casinos except among those actually playing (unlike [[craps]], [[roulette]] and [[Big Six wheel|wheels of fortune]] which have larger displays and so tend to attract more spectators).

==Ranging bet sizes and the Kelly criterion==
A mathematical principle called the [[Kelly criterion]] indicates that bet increases should be proportional to the player advantage. In practice, this means that the higher the count, the more a player should bet on each hand in order to take advantage of the player edge.  Using this principle, a card counter may elect to vary his bet size in proportion to the advantage dictated by a count creating what is called a "Bet ramp" according to the principles of the Kelly criterion.  A bet ramp is a betting plan with a specific bet size tied to each true count value in such a way that the player is betting proportionally to the player advantage with aims to maintain a constant risk of ruin for every bet made.
Taken to its ultimate conclusion, the Kelly criterion would demand that a player not bet anything at all when the deck doesn't offer a positive expectation; the "Wonging" strategy described above implements this.<ref>Axelrad (2010), pp. 258-259.</ref>

== Expected profit ==

Blackjack played with a perfect basic strategy typically offers a house edge of less than 0.5%, but a typical card counter who ranges bets appropriately in a game with six decks will have an advantage of approximately 1% over the casino. Advantages of up to 2.5% are possible at normal penetrations from counting 6-deck [[Spanish 21]], for the S17 or H17 with redoubling games.<ref>Walker (2008), p. 89</ref> This amount varies based on the counter's skill level, penetration (1 – fraction of pack cut off), and the number of betting units that the counter is able to spread from.  The variance in blackjack is high, so generating a sizable profit can take hundreds of hours of play. The deck will only have a positive enough count for the player to raise bets 10%-35% of the time depending on rules, penetration and strategy.

At a table where a player makes a $100 average bet, a 1% advantage means a player will win an average $1 per hand.  This translates into an average hourly winning of $50 if the player is dealt 50 hands per hour.

With typical bet ranging and typical Las Vegas six-deck rules, a player whose strategy yields an average profit of $50 per hour will likely face a standard deviation in the neighborhood of $1,400 per hour. Therefore, it is highly advisable for counters to set aside a large dedicated bankroll; one popular [[rule of thumb]] initially introduced by Thorp in Beat the Dealer dictates a bankroll of 100 times the minimum bet per hand.

Another aspect of the probability of card counting is that, at higher counts, the player's probability of winning a hand is only slightly changed and still below 50%.  The player's edge over the house on such hands does not come from the player's probability of winning the hands. Instead it comes from the increased probability of blackjacks, increased gain and benefit from doubling, splitting and surrender, and the insurance side bet, which becomes profitable at high counts.

Many factors will affect a player's expected profit while attacking a game, such as:
*The overall efficiency of a card counting system at detecting player advantage, this affects how often the player will actually play a hand at an advantage per period of time
*The overall efficiency at creating player advantage as a whole, a system may indicate a small advantage when in fact the advantage is much larger, this reduces the overall ROI of the system while in play.
*The rules of the game.
*Penetration will almost directly affect the magnitude of player advantage that is exploitable, and the rate that hands are dealt to a player at an advantage.
*The number of players seated at a table will slow game pace, and reduce the number of hands a player will be able to play in a given time frame.
*Game speed, table with side bets will be dealt at a slower pace than tables without them which will reduce the number of hands dealt over time.
*The use of an automatic shuffle machine or in rare cases, a dealer dedicated solely to shuffling a new shoe while another is in play, will eliminate the need for the dealer to shuffle the shoe prior to dealing a new one increasing game speed.

== Devices ==

A range of card counting devices are available but are deemed to be illegal in most U.S. casinos. In February 2009, the [[Nevada Gaming Control Board]] issued a warning that an [[iPhone]] card counting application was illegal in that state. Card counting with the mind is legal and usually more accurate than this application.

== Legal status ==
{{globalize|date=December 2010}}

===United States===
As of September 2012, card counting is legal under federal, state, and local laws in the United States as long as no external card counting device or person assists the player in counting cards.  It is however frowned upon by casinos.<ref name="bjlaw">Rose and Loeb (1998)</ref> Casinos continue to offer blackjack only because the vast majority of unskilled casual blackjack players more than make up for the small number of [[advantage players]] capable of reducing the casinos' edge. In their pursuit to catch card counters, casinos can sometimes misidentify and ban unskilled casual players whose betting style (or lack of) unknowingly mimics betting patterns of card counters.<ref>Zender (2006)</ref> 

Atlantic City casinos in the State of [[New Jersey]] are forbidden from barring card counters as a result of a [[New Jersey Supreme Court]] decision. In 1979 [[Ken Uston]], a [[Blackjack hall of fame|Blackjack Hall of Fame]] inductee, filed a lawsuit against an Atlantic City casino, claiming that casinos did not have the right to bar skilled players. The [[New Jersey Supreme Court]] agreed,<ref>See summary brief of [http://www.casebriefs.com/blog/law/property/property-law-keyed-to-singer/trespass-and-public-rights-of-access-to-property/uston-v-resorts-international-hotel-inc/ ''Uston v. Resorts International Hotel, Inc.; 445 A.2d 370 N.J. 1982'']</ref> ruling that "the state's control of Atlantic City's casinos is so complete that only the New Jersey Casino Control Commission has the power to make rules to exclude skillful players." As of 2011, New Jersey Casino Control Commission has not promulgated a regulation to the contrary. Accordingly, Atlantic City casinos are not allowed to bar card counters. In response to Uston's legal victory, Atlantic City casinos began adding decks, moving up shuffle points, and introducing other player-unfriendly rules to further decrease a skilled player's potential advantage.<ref name=bigplayer>Olsen (1981)</ref>

== Countermeasures ==
Casinos have spent a great amount of effort and money in trying to thwart card counters. Countermeasures used to prevent card counters from profiting at blackjack include:

*Harassment of suspected card counters by casino staff. This may be as simple as engaging a suspected card counter in a conversation to break their concentration.
*Decreasing penetration, the percentage of the cards dealt before a shuffle. This reduces the ability of a counter to take advantage of a high count that has developed.
*Assigning a high speed dealer to confuse the player or make the suspected counter more transparent to the people monitoring.
*Card-counter identification, using books of photos and [[facial recognition system]]s to "blacklist" known counters.
*Computerized scanners in blackjack tables that can identify counting systems when in use (such as [[MindPlay]]).
*Heuristic systems that keep a count and track players' bets, looking for increases/decreases matching rises and falls in the count.
*Computer systems used in surveillance rooms that surveillance staff use to target suspect players to quantify their threat to the house.
*Shuffling when a player increases their wager.
*Changing rules for splitting, doubling down, or playing multiple hands. This also includes changing a table's stakes.
*Flat betting a player or making it so they cannot change the amount they bet during a shoe.

Some jurisdictions ([[Nevada]]) have no legal restrictions placed on these countermeasures. Other jurisdictions such as [[New Jersey]] limit the countermeasures a casino can take against skilled players.<ref>{{cite web|url=http://rose.casinocitytimes.com/articles/1021.html |title=Dealing with Card Counters by I. Nelson Rose |publisher=Rose.casinocitytimes.com |date=2002-08-08 |accessdate=2009-03-20}}</ref> In the past, casinos would sometimes resort to harsher methods (up to and including physical assault) to deter card counters <ref>[http://www.blackjackforumonline.com/content/SpareRod.htm Blackjack Forum Volume XXIII #2, Summer 2003] - "Spare the Rod, Spoil the Card Counter" by Arnold Snyder - © 2003 Blackjack Forum</ref> – today the need to maintain good [[public relations]] and the likelihood of legal action dissuade casinos in most jurisdictions from such tactics.

Some of these countermeasures have a downside for the casino as well. Frequent shuffling, for example, reduces the amount of time that the non-counting players are playing and consequently reduces the house's winnings. Some casinos now use automatic shuffling machines to compensate for this, with some models of machines shuffling one set of cards while another is in play. Others, known as Continuous Shuffle Machines (CSMs), allow the dealer to simply return used cards to a single shoe to allow playing with no interruption.  Because CSMs essentially force minimal penetration, they remove almost all possible advantage of traditional counting techniques. In most online casinos, the deck is shuffled at the start of each new round, ensuring the house always has the advantage.

A pit boss who determines that a player is a card-counter might either "back off" the player by inviting them to play any game other than blackjack, or will ban them from the casino itself. In jurisdictions where this is not legal, such as Atlantic City, a pit boss can require the player to flat-bet and disallow players from entering in the middle of a shoe. Such countermeasures effectively remove any chance of gaining an advantage from card counting in multi-deck games. The player's name and photo (from surveillance cameras) may also be shared with other casinos and added to a database of card counters and cheaters (note: card counting is not cheating, but casinos still associate the two groups together) run for the benefit of casino operators. One such blacklist was known as the [[Griffin Book]], and was maintained by a company called [[Griffin Investigations]]. However, Griffin Investigations was forced into bankruptcy in 2005 after losing a libel lawsuit filed by professional gamblers.<ref>{{cite web|url=http://www.lasvegassun.com/news/2005/sep/13/griffin-book-producer-files-for-chapter-11-citing-/ |title=Griffin book producer files for Chapter 11, citing suit |author=Liz Benston |publisher=LasVegasSun |accessdate=2010-06-15}}</ref>

== Detection ==
{{Refimprove|date=August 2008}}

Monitoring player behavior to assist with detecting the card counters falls into the hands of the on-floor casino personnel ("pit bosses") and casino-surveillance personnel, who may use video surveillance ("the [[Eye in the sky (camera)|eye in the sky]]") as well as computer analysis, to try to spot playing behavior indicative of card counting; early counter-strategies featured the dealers' learning to count the cards themselves to recognize the patterns in the players.  In addition, many casinos employ the services of various agencies, such as Griffin Investigations, who claim to have a catalog of advantage players.  If a player is found to be in such a database, he will almost certainly be stopped from play and asked to leave regardless of his table play.  For successful card counters, therefore, skill at "cover" behavior, to hide counting and avoid "drawing heat" and possibly being barred, may be just as important as playing skill.

Detection of card counters will be confirmed after a player is first suspected of counting cards; when seeking card counters casino employees, whatever their position, could be alerted by many things that are most common when related to card counting but not common for other players.  These include:
*Large buy ins
*Large bet sizes
*Dramatic bet variation especially with larger bets being placed only at the end of a shoe
*Playing only a small number of hands during a shoe
*Refusal to play rated
*Table hopping
*Playing multiple hands

The strategy applied to the playing of hands can be used to detect a possible counter since very few players play perfect playing strategy, furthermore, card counters will play perfect playing strategy, then they will suddenly alter it and make unique strategy deviations that can be a dead givaway.  Plays such as splitting tens, doubling soft 18/19/20, standing on 15/16, and surrendering on 13/14 when basic strategy says otherwise, may be a sign of a card counter.

Extremely aggressive plays such as splitting tens and doubling soft 19 and 20 are often called out to the pit to notify them because they are telltale signs of not only card counters  but [[hole carding]], and most forms of advantage gambling.

== Technology for detecting card counters ==
Several automated systems have been designed to aid detection of card counters. The [[MindPlay]] system scans card values for the entire deck after shuffling just prior to play. The [[Shuffle Master]] Intelligent Shoe system scans card values individually as cards exit the shoe. Software called Bloodhound and Protec 21<ref>{{cite web|url=http://www.digitace.com |title=Digitace Website |publisher=digitace.com |date= |accessdate=2009-03-20}}</ref> allows voice input of card and bet values, which is used to determine the player edge. A more recent innovation is the use of [[RFID]] signatures embedded within the casino chips so that the table can automatically track bet amounts.<ref>{{cite web|last=Gilbert |first=Alorie |url=http://news.com.com/2100-7355_3-5568288.html |title=CNET News story, "Vegas Casino Bets on RFID" |publisher=News.com.com |date= |accessdate=2009-03-20|archiveurl=http://archive.is/GQaX|archivedate=2012-07-22}}</ref>

Automated card-reading technology has known abuse potential in that it can be used to simplify the practice of ''preferential shuffling'' — having the dealer reshuffle the cards whenever the odds favor the players. To avoid liability concerns, some blackjack protection systems have been designed to refrain from sending data over the network until the shoe has ended.<ref>[http://www.shufflemaster.com/index.php?option=com_k2&view=itemlist&layout=category&task=category&id=153&Itemid=4 Shufflemaster shuffling shoes for blackjack]</ref> Other vendors consider real-time notification to surveillance that a shoe is "hot" to be an important product feature.<ref>Aventura Technologies, [http://www.ati247.com/pdf/Real-Time%20Casino%20Solution_v01.2.pdf Real Time Casino Solution (PDF)], diagram 12, "Advantaged Play Server"</ref>

With card values, play decisions, and bet decisions conveniently accessible, the casino can analyze bet variation, play accuracy, and play variation.

''Bet variation.'' The simplest way a card counter makes money is to bet more when he has an edge. While playing back the tapes of a recent session of play, software can generate a scatter plot of the amount bet versus the count at the time the bet was made and find the trendline that best fits the scattered points. If the player is not counting cards, there will be no trend; his bet variation and the count variation will not consistently correlate. If the player is counting and varying bets according to the count, there will be a trend whose slope reflects the player's average edge from this technique.<ref>Arnold Snyder's ''[[Blackjack Forum]]'' periodical featured a printout that demonstrated this feature</ref>

''Play accuracy''. Normal players tend to make basic strategy errors. Card counters must accurately know exactly when to hit, stand, split, or double down. Software can verify the rate at which the player makes errors and calculate the resulting house edge.

''Play variation''. When card counters vary from basic strategy, they do so in response to the count, to gain an additional edge. Software can verify whether there is a pattern to play variation. Of particular interest is whether the player sometimes (when the count is positive) takes insurance and stands on 16 versus a dealer 10, but plays differently when the count is negative.

== History ==

American [[mathematician]] Dr. [[Edward O. Thorp]] is considered the father of card counting.<ref>{{cite web |url=http://www.blackjackapprenticeship.com/resources/history-of-blackjack/ |title=The History of Blackjack |author=Loudon Ofton|publisher=BlackjackApprenticeship.com |date= |accessdate=2013-03-09}}</ref> His 1962 book, ''Beat the Dealer'', outlined various betting and playing strategies for optimal blackjack play. Although mathematically sound, some of the techniques described no longer apply, as [[casino]]s took counter-measures (such as no longer dealing to the last card). Also, the counting system described (10-count) is harder to use and less profitable than the point-count systems that have been developed since. A history of how counting developed can be seen in David Layton's documentary film, ''[[The Hot Shoe]]''.

Even before the publication of ''Beat the Dealer'', however, a small number of professional card counters were beating blackjack games in Las Vegas and casinos elsewhere. One of these early card counters was Jess Marcum, who is described in documents and interviews with professional gamblers of the time as having developed the first full-fledged point-count system. Another documented pre-Thorp card counter was a professional gambler named Joe Bernstein, who is described in the 1961 book ''I Want To Quit Winners'', by Reno casino owner Harold Smith, as an Ace counter feared throughout the casinos of Nevada. And in the 1957 book ''Playing Blackjack to Win'', Roger Baldwin, Wilbert Cantey, Herbert Maisel, and James McDermott (known among card counters as "The Four Horsemen") published the first accurate blackjack basic strategy and a rudimentary card-counting system, devised solely with the aid of crude mechanical calculators—what used to be called “adding machines."

From the early days of card-counting, some players have been hugely successful, including Al Francesco, the inventor of blackjack team play and the man who taught [[Ken Uston]] how to count cards, and [[Tommy Hyland]], manager of the longest-running blackjack team in history.  Ken Uston, though perhaps the most famous card-counter through his ''60 Minutes'' television appearance and his books, tended to overstate his winnings, as documented by players who worked with him, including Al Francesco and team member Darryl Purpose.

In the 1970s and 1980s, as computing power grew, more advanced (and more difficult) card-counting systems came into favor. Many card counters agree, however, that a simpler and less advantageous system that can be played flawlessly for hours earns an overall higher return than a more complex system prone to user error.

=== Teams ===
{{more footnotes|date=May 2012}}
In the 1970s Ken Uston was the first to write about a tactic of card counting he called the Big Player Team. The book was based on his experiences working as a "big player" (BP) on Al Francesco's teams. In big-player blackjack teams a number of card counters, called "spotters," are dispatched to tables around a casino, where their responsibility is to keep track of the count and signal to the big player when the count indicates a player advantage. The big player then joins the game at that table, placing maximum bets at a player advantage. When the spotter indicates that the count has dropped, he again signals the BP to leave the table. By jumping from table to table as called in by spotters, the BP avoids all play at a disadvantage. In addition, since the BP's play appears random and irrational, he avoids detection by the casinos. The spotters, who are doing the actual counting, are not themselves changing their bet size or strategy, so they are relatively inconspicuous. 

With this style of play, a number of blackjack teams have cleared millions of dollars through the years. Well-known blackjack teams with documented earnings in the millions include those run by Al Francesco, Ken Uston, Tommy Hyland, various groups from the Massachusetts Institute of Technology ([[MIT]]) and, most recently, a team called "The Greeks." Ken Uston wrote about blackjack team play in ''Million Dollar Blackjack'' (ISBN 0-89746-068-5), although many of the experiences he represents as his own in his books actually happened to other players, especially Bill Erb, a BP Uston worked with on Al Francesco's team.  [[Ben Mezrich]] also covers team play in his book ''[[Bringing Down the House (book)|Bringing Down The House]]'' (ISBN 0-7432-4999-2), which describes how MIT students used it with great success. See also the Canadian movie ''[[The Last Casino]]'', the American movie ''[[21 (2008 film)|21]]'', which was based on Mezrich's book, and more recently the 2011 American movie ''{{IMDb title|1780862|Holy Rollers}}''.

The publication of Ken Uston's books and of his landmark lawsuits against the casinos, both stimulated the growth of blackjack teams (Hyland's team and the first MIT team were formed in Atlantic City shortly after the publication of ''Million Dollar Blackjack'') and increased casino awareness of the methods of blackjack teams, making it more difficult for such teams to operate. Hyland and Francesco soon switched to a form of shuffle tracking called "Ace sequencing." Also referred to as "cutting to the Ace," this technique involves various methods designed to spot the bottom card during a shuffle (ideally an Ace) and expertly cut the deck and play future hands to force the player to receive the Ace. This made it more difficult for casinos to detect when team members were playing with an advantage. In 1994, members of the Hyland team were arrested for Ace sequencing and blackjack team play at [[Casino Windsor]] in [[Windsor, Ontario]], [[Canada]]. It was documented in court that Nevada casinos with ownership stakes in the Windsor casino were instrumental in the decision to prosecute team members on cheating charges. However, the [[judge]] ruled that the players' conduct was not cheating, but merely the use of intelligent strategy.<ref name="blackjack2006">Snyder (2006)</ref>

=== Shuffling machines ===

The introduction of shuffling machines that "randomly" shuffle decks (or at least "pseudo-randomly"), have been introduced by most casinos to defeat cheating (dealers & players colluding) and card-counters. Continuous Shuffling Machines (CSMs), which allow dealers to return the cards played to a single shoe, in particular make it quite possible for cards that were just played on the table to be re-shuffled to the top of the shoe, effectively rendering all card-counting schemes as useless. See the section on [[Shuffling machine]].

==See also==
*[[Casino security]]

==References==
=== Notes ===
{{Reflist|colwidth=30em}}

=== Bibliography===
* {{cite book |last = Axelrad |first = Josh |authorlink =  |title = Repeat until Rich: A Professional Card Counter's Chronicle of the Blackjack Wars |edition =   |publisher = Penguin Press |location = New York |pages =  |series =  |year = 2010  |doi =  |lccn =  |oclc =  |isbn = 978-1-59420-247-6}}
* {{cite book |title=The Theory of Blackjack: The Complete Card Counter's Guide |author=Griffin, Peter |authorlink=Peter_A._Griffin |isbn=0-915141-02-7 |year=1988 |publisher=Huntington Press |location = Las Vegas |edition = 4th}}
* {{cite news|author=Eddie Olsen|date=April 18, 1981|publisher=''[[Philadelphia Inquirer]]''|title=Ken Uston: Big Player Without a Game}}
* {{cite book |last1 = Rose  |first1 = I. Nelson  |authorlink1 =   |last2 = Loeb  |first2 = Robert A.  |authorlink2 = |title=Blackjack and the Law |isbn=978-0-910575-08-9 |year=1998 |publisher=RGE Publishers |location=Oakland, CA |edition= 1st}}
* {{cite book  |last = Schlesinger  |first = Donald  |authorlink =   |title = Blackjack Attack: playing the pros' way  |edition = 3rd  |publisher = RGE Publishing
  |location = Las Vegas  |pages =   |series =   |year = 2005  |doi =  |lccn =  |oclc =  |isbn = 978-0-910575-20-1 }}
* {{cite book  |last = Snyder  |first = Arnold  |authorlink =   |title = The Big Book of Blackjack  |edition = 1st  |publisher = Cardoza Publishing  |location =  New York |pages =   |series =   |year = 2006  |doi =  |lccn =  |oclc =  |isbn = 1-58042-155-5}}
* {{cite book |title=Beat the Dealer: A Winning Strategy for the Game of  Twenty One | last = Thorp |first = Edward O.|authorlink=Edward O. Thorp|isbn=0394-70310-3 |year=1966 |publisher=Vintage Books |location = New York}} 
* {{cite book  |last = Walker  |first = Katarina  |authorlink =   |title = The Pro's Guide to Spanish 21 and Australian Pontoon  |edition =   |publisher = Maven Press  |location = New York  |pages =   |series =   |year = 2008  |doi =  |lccn =  |oclc =  |isbn = 978-1-4357-1065-8}}
* {{cite book  |last = Zadehkoochak  |first = Mohsen  |authorlink =   |title = The Book of British Blackjack  |edition =   |publisher = Medimage  |location = Cockfosters, England  |pages =   |series =   |year = 1992  |doi =  |lccn =  |oclc =  |isbn = 1-897728-00-X}}
* {{cite book  |last = Zender  |first = Bill  |authorlink =   |title = Advantage Play for the Casino Executive  |edition =   |publisher =   |location =   |pages = 
  |series =   |year = 2006  |doi =  |lccn =  |oclc = 156916229 |isbn = }}
==Further reading==
* {{cite book  |last = Snyder  |first = Arnold  |authorlink =   |title = Blackbelt in Blackjack: Playing 21 as a Martial Art  |edition = Revised  |publisher = Cardoza Publishing  |location =  New York |pages =   |series =   |year = 2005  |doi =  |lccn =  |oclc =  |isbn = 1580421431}}

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[[Category:Blackjack]]
[[Category:Gambling terminology]]