Metallicity determination of the star HD 122563. Top panel: line-to-line Fe abundances computed with υ_mic = 2.5 km s⁻¹ as a function of the reduced equivalent width. Grey and red dots represent Fe I and Fe II lines, respectively. The solid dark red line is the trend of all Fe I and Fe II measurements. The black dashed and red dotted lines are the trends of Fe I and Fe II measurements, respectively. The shade represents the dispersion. Bottom panel: for HD 122563, metallicity as function of υ_mic colour-coded by the slope of the trends in the υ_mic–[Fe/H] plane.