Histograms of the output values of the diagnostics used to derive the stellar parameters for the 89 stars in our combined sample. Panel a: slope S_χ of FeI abundance vs. excitation potential χ used to derive the effective temperature T_eff (solid blue curve, bottom x scale). The corresponding peak-to-peak values of the spread in iron abundance (ΔA(FeI)_p2p, see Eq. (1)) are plotted as an open orange curve (top x scale). Panel b: slope S_EWR of the relation between FeI abundance and reduced EW EWR = log(EW/λ), which ranges between −5.5 and −4.5, and is used to constrain the microturbulent velocity v_turb (solid blue curve, bottom x scale). Also here, the corresponding peak-to-peak values of the spread in iron abundance (ΔA(FeI)_p2p, see Eq. (1)) are plotted as an open orange curve (top x scale). Panel c: difference between FeI and FeII, the minimisation of which is used to determine the surface gravity log(g). The mean and standard deviation of the distribution are 0.007 and 0.033 dex, respectively, indicating excellent agreement between the derived FeI and FeII abundances, and hence gravity, with no appreciable systematic errors.