Ratio of sulfur abundance to mean metallicity [S/M] as a function of the mean stellar metallicity [M/H] for the best derived abundances. Top two panels: dispersion smaller than 0.05 dex and/or high-S/N spectra (top panel) and the same criteria plus a selection of stars having at least three measurements of the three individual S I lines (golden sample, second panel from top). Bottom two panels: behaviour of [α/Fe] and [S/α] vs. mean metallicity for the golden sample.