Comparison between T_eff and [Fe/H]_e obtained with GSL and AP18 grids. Top panel: difference between T_eff (ΔT_eff(AP18-GSL), computed by subtracting the GSL results from the AP18 results) as a function of T_eff values with GSL. Bottom panel: difference of equivalent iron abundance (Δ[Fe/H]_e) as a function of the iron abundance with GSL. The dashed blue line shows the expected bias due to the different level of α-element enhancement in the two grids (0.4 vs. 0.5 dex, see the text for details). In both panels we report the mean and rms of the differences.