How Do People Count Cards In Casinos?

   Card counting is a practice that has been occurring in casinos since the 1960s, when books were first published on the topic. Some people, particularly teams of mathematically minded MIT students, made millions by using card counting techniques. The practice of card counting involves the player counting cards to gain an advantage over the casino, enabling them to beat the odds and increase their winnings. Many people think that card counting involves memorizing every card that is played so that the next card to be played is definitively  known, but this is inaccurate; card counting is actually the process of remembering how many high-numbered cards have been played in relation to low-numbered cards, which gives the player an indication of the type of cards that are left in the deck.
   There have been more than a hundred card-counting techniques, although complex systems of card counting are prone to human error. The most common and successful simple method used is the "Hi-Lo Count." In this system, only one number needs to be remembered at any time. "Plus one" is assigned to cards two, three, four, five and six and "minus one" is assigned to cards ten, jack, queen, king and ace. "Zero" is assigned to seven, eight and nine, which are known as neutral cards. The player counts the cards as they are played by adding or subtracting one for each card, depending on it's assigned value. A overall positive value means that there is likely to be a greater proportion of high cards in the deck. This gives the player an advantage in blackjack, for instance---a game in which counting systems are most commonly used---because the dealer is more likely to receive a high card and go bust above twenty-one (the dealer being required by the rules not to sit below seventeen). When the decks are reshuffled, the count begins again from zero.
   Card counting does not help a player to win more hands; it simply means that he or she alter the size of his or her bet, depending on the count. If the count is low (i.e., below zero), the player will bet low. If the count is high (generally plus two or more), the player will bet high. In the long run, this should result in the player winning more money than he or she loses.
   While card counting isn't illegal, unless a hidden mechanical device is used, the casino environment makes counting more difficult. The number of decks used per shuffle has increased, the casinos are noisy and full of distractions, and surveillance systems monitor notorious card counters, who, once spotted, are then removed or refused entry to casinos.