[Fe/H] abundance ratios derived from Fe I lines for the star NGC 6752−23, plotted versus the excitation potential (top) and line equivalent width (bottom). Linear fits to the data are shown as solid lines. Note that there is a slight correlation between the best-fit slopes in the two panels: adjusting the temperature by zeroing the slope in the upper panel slightly changes the slope in the lower panel, while changes to the microturbulence velocity influence the slope in the upper panel. This correlation does not allow us to obtain zero-valued slopes in both panels simultaneously. The adopted atmospheric parameters of this star are T_eff = 4956 K, log g = 2.35, ξ_t = 1.28 km s^-1, and [Fe/H] =  −1.57.