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What is ace tracking? Ace tracking relies on the fact that when a hand is over, the croupier scoops up the cards in a smooth, predictable motion, in which each card slides under its neighbour and all are put in the discard box in the exact order in which they were originally dealt. An ace tracker memorises the two cards that go underneath each ace.
But aren't the cards shuffled before being redealt? Yes, and after the shuffle the cards will be separated out somewhat. But they seldom go far. When the cards are re-dealt, therefore, and you see your two-card sequence, you know that an ace will follow almost immediately after.
A player with an ace as the first card has 52% advantage