(V − I),V colour-magnitude diagram from our photometry. The location of RR Lyrae (filled circles, RR0 in red, RR1 in green), SX Phoenicis (green triangles), U Geminorum (blue square), eclipsing blue straggler (black open square) and other variables of uncertain type (green filled squares) are shown. On the right of the plot, typical error bars are plotted for different magnitude levels. Also plotted are isochrones from VandenBerg & Clem (2003) for ages of 9, 10.5, 12, 13.0 (our best-fit isochrone), 13.5 and 15 Gyr.