Ratio of the EW of He I 7065 to He II 5412 as a function of spectral type for the low-metallicity models calculated in the present study, the solar metallicity models of Martins & Palacios (2017) and observations of Galactic stars collected from archives (open red circles – see text for details). Left panel: all data points shown. When no unique spectral type was assigned to a model (e.g., O6−6.5) the average was used (i.e., O6.25). Numbers above ten correspond to B stars (with ten being B0, and 10.5 being B0.5). Right panel: same as left panel but showing only the average value of the EW ratio for each spectral type. In that panel the spectral types of the 1/5 Z_⊙ (1/30 Z_⊙) models have been shifted by +0.03 (−0.03) for clarity. We also considered only “official” spectral types, that is, we excluded for example 6.25 when a spectral type O6−6.5 was assigned to a model.