For a fixed Mg non-LTE abundance (dotted line), the Mg abundance that would be derived in LTE shown as function of T_eff based on the 5528 (top) and 5711 (bottom) Å lines. Colour lines connect model atmospheres with the same log g(cm/s²). log g varies from 0.5 (blue) to 5.0 (red) dex in steps of 0.5 dex. The black points correspond to the RGB, bRGB, SGB and TOP models used in Fig. 4.