Ratio ﹩\eta _{0}/ \Delta \lambda ^{2}_{D}﹩ for the Fe I line at 6301 Å for two model atmospheres: HSRM (continuous line; Gingerich et al. 1971) and the M model (dashed line) from Maltby et al. (1986). The ordinates are given in Å⁻². Compare this to the typical value of 6250 Å⁻² used in the thermodynamic Milne‐Eddington atmospheres.