Impact of metallicity for the determination of atmospheric parameters in the T_eff vs log g (left) and log [n(He)/n(H)] vs T_eff (right) plane. Results derived for standard metal composition (z=0) are marked by blue crosses. The red and green symbols indicate the parameters derived for these same stars when fixing the metal content to half (z=−0.3) and twice (z=+0.3) the standard composition, respectively, and are connected by black lines to highlight the shifts. The position of the EHB band (dashed and dotted lines) and the zero-age helium main sequence (dot-dashed line, marked with the stellar mass) is also shown in the T_eff vs log g plane.