The spread of low-cost pocket calculators even to the elementary-school level was bound to be followed by a wave of children's books explaining them. After the puffery of Bitter and Metos (p. 429, J-109), this one seems responsible. Mims avoids the redundant instructions as to which key to punch for which function; he compresses the same games and recreations into a more appropriate two pages; and if he doesn't really explain how a calculator works, he does give a reasonable description of its ""insides"" and the function of such commonly mentioned items as circuits, wafers, and chips. More thorough are the earlier sections which teach you how to add, subtract, multiply, and divide on an abacus (you can follow the lesson easily even if you don't have an abacus on hand) and then, clarifying logarithms, show just as painlessly how to make and use a slide rule. Overall, it's slight, but straightforward.