Several schemes use modular arithmetic to append a check digit to product identification numbers for error detection. Some schemes are discussed, including ones for money orders and library books. Then a foolproof method is presented. (MNS)

Numerical inaccuracies, which occur in many ordinary computations, can create serious problems and render answers meaningless. Cancellation and accumulation errors are described, and suggestions for experimentation are discussed. (MNS)

Brief articles are included on exploring mathematical patterns, with two computer programs listed for finding happy numbers; a simple periodic function in trigonometry; and comments on humorous student errors. (MNS)