Difference between node values and reference values in example case of the CAUP analysis of Mg I measured in the HR21 spectrum. Top row: differences against [Fe/H] for the full sample (left-black), the giants (middle-red), and the dwarfs (right-blue). Middle row: same but against log g. Bottom row: same but against T_eff. The differences as median differences calculated per bins are shown as orange points with error bars. The linear fit (orange dot-dash) and quadratic fit (red dot-dash) are shown in each case.