Data for stars observed in NGC 5824. The upper panel shows the observed heliocentric velocity plotted against V − V_HB. The dotted line is the cluster velocity given by the Harris catalogue, the dashed line is the mean velocity for the 17 stars selected as cluster members. The sole star identified as a radial velocity non-member is plotted as an  × -sign. The lower panel shows ΣW against V − V_HB for the same stars. The dot-dash line is the fit of the calibration relation to the cluster member points (filled circles). Shown also are the calibration lines for the standard clusters M 15, NGC 4372, NGC 6397, M 10, M 5 and M 71 (in order of increasing ΣW). The significant scatter in the NGC 5824 member data suggests the presence of an intrinsic metallicity dispersion.