The pupils can verify their prediction by means of the calculator. The systematically arranged chart can then be used to get the pupils to offer conjectures about how it is possible to tell directly from the given numbers the number of steps to zero. It is immediately clear that we get zero after one step if and only if at least the hun dreds digit and the ones digit of the num ber are identical. It is advisable to start the real investigation with the questions for the two step numbers"; that is, the numbers for which the second difference is zero.