A card-counting system for blackjack in which you keep track of the exact number of both high (ten-value) and low cards that have appeared in play, and the ratio, to indicate to you the favorability of the deck.
When the deck is rich in tens and face cards, it favors the player, since the dealer is more likely to bust by having to hit on a stiff hand (12 through 16) while a player has the option to stand on a similar hand. That’s what you want to know: when is the deck rich, so you can increase your bet then. A good card-counting system is one that counts all the ten-value cards. This fractional 10-count system for single-deck games counts how many tens have appeared, and balances this number with the number of low cards that have appeared. Since there are 16 ten-value cards, the group of low cards must also be 16. You choose the contents of your low-card group according to which seems to you more influential in play — 3 through 6, or 4 through 7. Aces are not counted, and neither are 2, 8, or 9.
The top half of your fraction always represents the low card count, and the bottom, or second part of the fraction refers to the high card count. You start with 16/16 because that is the total of both, then subtract one when a card of either group appears. Suppose you enter a game and see 6 low cards and 3 high cards. Your ratio would be 10/13. In subsequent hands, you simply keep subtracting from each part of that fraction. The key is this: a smaller fraction is more favorable to you. That 10/13 would indicate a deck beginning to favor you, but an even smaller fraction, like 7/13, would definitely mean you should increase your bet. When the fraction equals a number greater than one, like 12/9, the deck is unfavorable and you should decrease your bet to your single unit or simply sit out a hand or two.