Dustin Hoffman was the perfect card counter in the movie “Rainman.” Hoffman plays an idiot-savant with a knack for winning in casinos. Media often makes it seem card counting is illegal with people on television quickly becoming persona non grata when a casino catches on. However, card counting is legal despite its unpopularity in the world’s casinos. But because casinos are private property, owners do have the right to kick you out.

Blackjack became the first card game publicly identified as one in which counting cards could be used to beat it. Casinos began seeing their profits drop and put in place measures to prevent it such as using multiple decks and shuffling often.

There are a number of ways to count cards, one of the easiest being a system called Hi-Lo. In this method, a player assigns a value to each card. Cards from two through five become +1; seven through nine are zero; tens, aces and face cards are -1. The player adds those values, the result being an indicator of the number of tens and aces left in the deck relative to smaller cards. If, after a hand, the total value is positive, the cards left in the deck run in your favor.

If there are multiple decks left in the shoe, a card counter need only divide his running count by the number of decks remaining. If you are playing a six-deck game and there are four decks remaining in the shoe, ending a hand with -4 becomes -1.

The card counter can use this information to know when to raise bets and when to lower them. With this edge the house advantage can turn into 1.5-percent odds in your favor.