Surface-gravity differences as a function of the atmospheric parameters. The size of each symbol is inversely proportional to log ɡ_iso. The points are coded in red or grey depending on the Mg I line (5172 Å or 5183 Å) used to compute log ɡ_Mg log ɡ_iso In the top panel, the offsets and ± 1σ dispersions are represented by the dashed lines and error bars, the values of which are −0.35 ± 0.21 for the line at 5172 A (in red) and −0.33 ± 0.19 for the line at 5183 Å (in grey). Individual log ɡ values are listed in Table A.1. Error bars in the middle and bottom plots are the quadratic sum of the errors of log ɡ_iso and those of log ɡ_Mg