log L as a function of decreasing core hydrogen mass fraction, in logarithm, for Z_init = 0.014 models of, from bottom to top, 1.0, 1.1, 1.16, 1.18, 1.2, 1.22, 1.24, 1.26, 1.28, 1.3, 1.4 and 1.5 M_⊙. The locations of the three reference points within the MS are shown by filled circles on each track. The dashed lines denote tracks for which the reference points are defined by fixed values of X_c(H) (see Sect. B.1.2).