During the course of a blackjack shoe, the dealer exposes the dealt cards. Players can infer from their accounting of the exposed cards which cards remain. These inferences can be used in the following ways:
Players can make larger bets when they have an advantage. For example, the players can increase the starting bet if many aces and tens are left in the deck, in the hope of hitting a blackjack.
Players can deviate from basic strategy according to the composition of their undealt cards. For example, with many tens left in the deck, players might double down in more situations since there is a better chance of getting a good hand.
A card counting system assigns a point score to each card rank (e.g., 1 point for 2–6, 0 points for 7–9, and −1 point for 10–A). When a card is exposed, a counter adds the score of that card to a running total, the 'count'. A card counter uses this count to make betting and playing decisions. The count starts at 0 for a freshly shuffled deck for "balanced" counting systems. Unbalanced counts are often started at a value that depends on the number of decks used in the game.
Blackjack's house edge is usually around 0.5–1% when players use basic strategy.[19] Card counting can give the player an edge of up to about 2%.[20]: 5
Card counting works best when a few cards remain. This makes single-deck games better for counters. As a result, casinos are more likely to insist that players do not reveal their cards to one another in single-deck games. In games with more decks, casinos limit penetration by ending the shoe and reshuffling when one or more decks remain undealt. Casinos also sometimes use a shuffling machine to reintroduce the cards whenever a deck has been played.
Card counting is legal unless the counter is using an external device,[20]: 6–7 but a casino might inform counters that they are no longer welcome to play blackjack. Sometimes a casino might ban a card counter from the property.[21]
The use of external devices to help count cards is illegal throughout the United States.[22]
Shuffle tracking
Main article: Shuffle tracking
Another advantage play technique, mainly applicable in multi-deck games, involves tracking groups of cards (also known as slugs, clumps, or packs) through the shuffle and then playing and betting according to when those cards come into play from a new shoe. Shuffle tracking requires excellent eyesight and powers of visual estimation but is harder to detect; shuffle trackers' actions are largely unrelated to the composition of the cards in the shoe.[23]
Arnold Snyder's articles in Blackjack Forum magazine brought shuffle tracking to the general public. His book, The Shuffle Tracker's Cookbook, mathematically analyzed the player edge available from shuffle tracking based on the actual size of the tracked slug. Jerry L. Patterson also developed and published a shuffle-tracking method for tracking favorable clumps of cards and cutting them into play and tracking unfavorable clumps of cards and cutting them out of play.[24][25][26]
Identifying concealed cards
The player can also gain an advantage by identifying cards from distinctive wear markings on their backs, or by hole carding (observing during the dealing process the front of a card dealt face-down). These methods are generally legal although their status in particular jurisdictions may vary.[27]
