Black solid histogram: Relative fraction of stars as a function of their helium content on the lower RGB in the models of Chantereau et al. (2016) and for an age of 13 Gyr. Blue solid line: Linear interpolation of Chantereau’s distribution between Y = 0.248 and 0.290, and extrapolation up to Y = 0.400. Red dashed histogram: Adopted distribution based on the previous interpolation and re-scaling so that the sum of relative fractions is equal to 1.