This guide lays out the computational methods for `d' with a variety of designs including factorial ANOVA, ANCOVA and repeated measures ANOVA; `d' divides the observed effect by the standard deviation of the dependent variable. Throughout, the computations are illustrated on the same data, a comprehensive set of simulated observations on air traffic controllers. The authors also raise important theoretical issues including a discussion of `off-factors' in arriving at effect size as well as questions of research practice.