A Man for All Markets: Beating the Odds, from Las Vegas to Wall Street

by Edward O. Thorp

One of the best compromises between ease of use and profitability was to count the small-value cards (2, 3, 4, 5, 6) as +1 as they are seen during play, intermediate cards (7, 8, 9) as 0, and large-value cards (10, J, Q, K, A) as −1.