Various quantities of our 16 M_⊙ stellar model computed with α_ov = 0.11 after core hydrogen depletion as a function of the internal mass coordinate. The model is undergoing hydrogen shell burning, as indicated by the relative rate of nuclear energy production (black dotted line). The hydrogen mass fraction is shown in green. The part of the hydrogen profile that was used to fit the H/He gradient dX/dQ (see main text) is shown with a dashed line; the rest is shown with a dot-dashed line. The resulting fit is shown as a straight red line. The semiconvective region, where the radiative temperature gradient ∇_rad exceeds the adiabatic temperature gradient ∇_ad in the presence of a stabilizing mean molecular weight gradient, is shaded in blue.