Entropy vs. density shown for different stellar parameters without and with normalization (a) and b), respectively). Each panel shows models with the same surface gravity, log g, and metallicity, [Fe/H], but different effective temperature, T_eff (orange/brown lines). Furthermore, the location of the optical surface, τ_Ross = 1, and maximum in the entropy gradient, ds | _max, are indicated (circle and triangle, respectively). In the left figure, the adiabatic entropy, s_ad, values are also shown (horizontal dotted lines). We note the differences in the axes between the top and bottom panels in a).