This very popular version of Gin Rummy is just like the original except for one key rule that requires even more skill of the player: The rank of the upcard fixes the maximum number of points with which a player may knock in that deal. Thus, if the upcard is a five, the knocker must have 5 points or less. Face cards count 10. When an ace is the knock card, neither player may knock with a count of 1 point; instead, each must play for a gin hand. An additional rule, often played, is that when the upcard is a spade, all scores accruing from that deal are doubled.
If the upcard is not taken by either player, it is usually set aside near the stock, so that both players can refer to it during play. If the upcard is taken by either player, the opponent may, at any time, ask what the upcard was, and the other player is required to give this information.