Temperature stratification and monochromatic optical depth τ_ν = 2/3 as functions of depth, where m is the column density, for NLTE models defined by T_eff = 82 000 K, log g = 6.4, and log N(He)/N(H) = −1.0. The temperature structure is shown for three model atmospheres with different compositions: with only H and He (black, dotted), with the metallic abundances of BD+28°4211 (red, dashed), and with ten times solar abundances (blue, solid). The τ_ν = 2/3 curve is from the latter model and shows wavelength intervals corresponding to the Balmer line series.The wavelength sampling of this curve is about 0.3 Å.