Run of temperature (left panels), logarithm of the gas pressure (middle panels), and logarithm of the electron number density (right panels) as a function of log τ_Ross for the model atmospheres of a dwarf star (T_eff=6500 K and log g=4.5, upper panels) and a giant star (T_eff=4500 K and log g=1.5, lower panels). The colour-coding is according to the metallicity of [M/H]. We adopted [α/Fe]=+0.0 dex for all the models.