Imagine a situation where the player has two starting cards for a total of 16, while the dealer’s open card is 7. If the player had any way of knowing that the next card is 5, the most beneficial move would consist of folding. The most likely outcome is for the player to win, and when this is the most likely outcome, smart players want to have as much money as possible at the table. The action of doubling generates this result and becomes the most obvious strategy in this situation.
However, most deviations from the strategy are not so obvious. The most common is based on the composition of the deck, which means that the player depends on knowing which cards have been played to determine which ones are still to be played. The player does not need to memorize all the cards that come out of the deck; this is practically impossible, especially in six-deck decks, which have a total of 312 cards. A much more elegant approach should be taken.
The simplest card counting system, and therefore the one subject to the fewest errors, is the Hi-Lo counting system. The Hi-Lo count assigns values to the cards. All cards from 2 to 6 have a value of +1. Cards 7, 8, and 9 have a value of 0, and aces, tens, and shapes have a value of -1.
The cards are added after each round, and the total is calculated. This is called a “checking account.” The current account value is requested for the number of decks remaining to play (this number can be deduced by looking at the cards in the discard deck and calculating the number of decks still remaining). The result of requesting the current account for the remaining decks is known as the “real account.” The actual count is a normalization of the ratio of high cards to low cards, or vice versa, left in each deck (on average). For example, if there is a checking account of +15 and three decks have been played from a deck of six, the actual count is +5 (15 in three equals five).
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