Left: differences between the age estimates obtained by adopting the grid with ΔY/ ΔZ = 5 (helium-enhanced) and that with ΔY/ ΔZ = 2 (standard). The red dashed line marks the mean of the differences, while the solid red line is a LOESS smoother of the data (see text). Right: empirical cumulative distribution functions for the upper limits of the estimated ages obtained by SCEPtER assuming the standard initial helium value (black line), the helium-enhanced scenario (blue line), and for the ages estimated by Bensby et al. (2013) (red line).