Upper panel: position of the targets in the temperature-gravity plane. Empty and filled circles are as in Fig. 1. The canonical zero-age and terminal-age HB for canonical stars are shown with full lines, and for analogous helium-enriched (Y = 0.33) models are indicated with dashed lines. The zero-age main sequence of solar chemical composition of Salasnich et al. (2000) is shown as dotted line. Middle and lower panels: comparison of stars in M 22 (same symbols as the upper panel) and members of NGC 6752, M 80, and NGC 5986 (open, grey diamonds), and ω Cen (open, grey stars). The vertical coordinate is the difference between the stellar gravity and the corresponding value of the canonical ZAHB at the same temperature. The full and dashed curves are the same as in the upper panel.