Comparison of thermal and pressure structure of 5250 K MARCS models with specially computed ATLAS 12 models. The top panel shows the temperature variation with the logarithmic Rosseland opacity, the middle panel the gas pressure variation, and the bottom panel the electron pressure variation. The MARCS models have normal helium abundance and different gravities (log g = 3.5 dex plotted as a dotted line and log g = 4.0 dex as a dashed line). The ATLAS 12 models have normal helium (thin continuous line) and enhanced helium (thick continuous line) at a fixed gravity of 3.7 dex.