Metallicity versus α-elements over iron abundance ratio for the HQ EHS sub-sample with high-quality chemical parametrisation (see text for details), colour-coded with their derived mass. The EHSs without published mass are plotted in grey. The Solar location is shown by the intersection of the dotted lines. The red line indicates a possible separation between the thick (high-α) and the thin (low-α) discs based on chemical criteria from Santos-Peral et al. (2021, see text for more details).