Results of 131 stars from Renson's (1991, Cat. <III/162>) catalogue of Ap and Am stars observed with the {Delta}-a system are presented. With few exceptions the probability division of Renson for membership in the CP2 group of peculiar stars is nicely reflected by peculiar values of {Delta}-a. Comparison with already available {Delta}-a values yields slightly larger values due to a minor shift in the g_1_ filter sampling the depression. For a description of the {Delta}-a and Stroemgren photometric system, see e.g. <GCPD/75> and <GCPD/04>, respectively.