Metallicity distribution of Hercules stars (dashed lines) according to a) Adén et al. (2009a); b) Adén et al. (2011); c) Musella et al. (2012); and d) Kirby et al. (2013). The shaded histograms show the metallicity distributions of the PM-selected stars. Weighted mean and dispersion values are also labelled for the original (on the left) and selected (on the right) distributions, respectively. Panel e): comparison of the whole sample of [Fe/H] measurements available in the literature before (dashed histogram) and after (shaded histogram) the PM selection (see text for more details).