Comparison of stellar abundance ratios [Mg/Fe] vs. [M/H] derived for the strong saturated line 5183.6 Å, colour-coded by stellar effective temperature (top row) and surface gravity (bottom row), after carrying out the continuum placement in three different local normalisation intervals around the line. Left:Δλ_norm ∼ 15 Å, typical local continuum interval applied in the literature for strong lines. Middle:Δλ_norm ∼ 10 Å. Right:Δλ_norm ∼ 6 Å, narrow normalisation interval (∼ twice the FWHM of the line in solar-type stars).