The goal of the game is to lead the opposite player to obtain a negative number. To accomplish it, players should choose strategic numbers from the keypad so that their opposite loses the game. But chooses obey to rules. The Calculator has 9 keys arranged in 3 columns and 3 rows. The keys bear random numbers from 1 to 9. A number, usually over 30, is selected on the indicator. The first player can push any of the nine keys thus decreasing the indicator number by the value of the pressed key. The second player can push any of the three keys in the column used by the first player, and then the first player can choose any key of the row previously used by the second player, and so on. The player which gets a negative number on the indicator loses. And so the challenge is on!