Root mean square magnitude deviation versus mean magnitude for all stars for which photometry was obtained. Plots are for the V-band (top) and I-band (bottom). Classified variables are marked as filled circles, with RR Lyrae in red, SX Phoenicis and blue stragglers in light green, U Geminorum in blue, and variables of unknown type as dark green triangles. Non-variable objects previously catalogued as variable in the literature are marked with red crosses.