Illustration of the three methods employed in the case of the differential analysis of α Cen A withthe line list of Bensby et al. (2014). Upper panels: unconstrained analysis requiring both excitation and ionisation equilibrium of iron; middle panels: constrained analysis assuming excitation balance of Fe I; bottom panels: constrained analysis assuming ionisation balance of iron. The dotted horizontal lines indicate the mean iron abundances, while the red dashed lines show the fit to the Fe I abundances as a function of LEP.