Edge sorting

Edge sorting is a technique used in advantage gambling where a player determines whether a face-down playing card is likely to be low or high at casino table games by observing and exploiting subtle unintentional differences on the backs of some types of card, after persuading a croupier to cooperate by unwittingly sorting the cards into low and high. Many packs of cards produced by manufacturers have unintentional edge irregularities. Typically all the backs of the cards in such a pack are identical, but the two long edges of each card are consistently distinguishable: the pattern is not symmetrical to a 180° rotation (half a full turn). During the course of a game, a player will ask the dealer, a casino employee, to rotate some face-up cards, perhaps saying they feel it will bring them luck. The dealer does not realise that cards are being turned so that low cards, typically, 6, 7, 8, or 9 are one way round, high cards the other way round, and that the edges are different. The dealer is also asked to shuffle the cards with an automatic shuffler, which does not change the orientation as a manual shuffle may do. The dealer is not obliged to comply with these requests, but will usually do so if thought to be due to gamblers' superstition or mistrust. Over the course of a game, low cards will tend to be oriented one way, high cards the other. Once a significant proportion of cards have been rotated, any player who knows this can gain a statistical edge more than outweighing house edge by using the knowledge whether the card to be turned is likely to be low or high.