In this study we proposed that understanding of interrelations among criterion measures can be improved by differentiating between measures of typical and maximum job performance. We offered defining characteristics of typical and maximum performance measures and requirements for a fair examination of relations between the two. Typical and maximum performance measures of the speed and accuracy with which supermarket cashiers process items were obtained from two large samples (Ns = 635 and 735) of cashiers from 12 supermarket chains. Relatively low correlations between typical and maximum performance measures were found. We discuss the implications of these findings for the use of maximum performance measures as criteria in the validation of selection systems and for the understanding of the impact of ability and motivation on job performance.