Top panel: specific entropy near the surface of several 1D stellar models and one 3D RHD simulation. The models and simulation all share the same surface parameters (﹩\mathrm{log}g=4.30﹩ and ﹩\mathrm{log}{T}_{{\rm{eff}}}\;=\;3.76﹩) and chemical composition (Z = 0.001, X = 0.754), but the 1D models are computed with different mixing length parameters, and so have different envelope entropy (s_ad). The simulation does not contain a mixing length parameter, so the specific entropy is determined self-consistently and uniquely. Bottom panel: contours of adiabatic entropy (s_ad) in the ﹩\mathrm{log}g﹩–﹩\mathrm{log}{T}_{{\rm{eff}}}﹩ plane, as determined by the 3D simulations of Magic et al. The contours of s_ad (ranging from 16 · 10⁸ to 24 · 10⁸ erg s⁻¹ K⁻¹ from the lower left to the upper right) are equivalent to contours of constant polytropic K (see, e.g., Kippenhahn & Weigert 1990) and denote the convective envelope adiabats. Evolutionary tracks for a range of stellar masses (M_⊙ = 0.75–1.40), all with the same composition parameters, and with the same constant value of the mixing length parameter α, are shown for reference.