Each of two players make up a sequence of four unique digits. The players then compete in trying to guess eachother's sequence.

In response to a guess one tells the opponent how many digits are in the right place and how many are in the wrong place. For each digit in the right place one gives an H (hit) and for each digit in the wrong place one gives a T (touch).

So if you play aginst the computer and your sequence is 0627 and the computer guesses 2690 then the result you give the computer is HTT. You also make your guess, for example 1234, on the sequence the computer is "thinking" of. See the example below.