Metallicity distributions of the HPMS samples (Fig. 1) binned by L_Z. In all columns except Col. (a), stars belonging to the low-α and high-α sequences are represented by red and blue histograms, respectively, while the green histogram indicates the uncertainty range due to variations in the α-based division (see text for details). To guide the eye, vertical dashed lines mark the median [Fe/H] of all stars within 1500 < L_Z < 1750 kpc km s⁻¹ in each sample. Cols. (d) and (e) refer to the high-resolution samples from GALAH and APOGEE, respectively.