Most scientists now own, or have access to, an electronic calculator and appear to have absolute faith in the answers it gives. However, these calculators have design limitations which for some data sets will affect the accuracy of the calculations and so produce incorrect results. In statistics work, corrected sums of squares and products, needed for Analyses of Variance and Regression Analyses, can be affected. The first two sections of this paper describe these limitations and illustrate how they can affect the result of calculating the variance of a particular data set. A simple procedure is then described that will help overcome the problem. Finally, in anticipaion that the micro-computer will eventually replace the calculator as the main mathematical tool, a more general procedure is given for calculating the sums of squares and products.