The V filter amplitude – period (P) Bailey diagram for our observations (coloured symbols) and the observations of M 31 RR Lyr from Sarajedini et al. (2009) and Brown et al. (2004) as grey and magenta symbols. The Oosterhoff type loci, OoI (dashed) and OoII (dot-dashed), are shown (from Clement 2000). For the RR Lyr the triangles are first-overtone pulsators and the circles are fundamental pulsators. RR Lyr two-filters are plotted in red and only in one-filter in orange. Anomalous Cepheids and Population II Cepheids are indicated with squares (green) and stars, respectively.