α-elements over iron abundance as a function of metallicity for four different sub-samples of stars with increasing errors in the abundance determination. Panel a) shows the results for stars with errors in [M/H] and [α/Fe] smaller than 0.07 dex and 0.03 dex, respectively (209 stars). Panel b) shows the results with errors smaller than 0.09 dex and 0.04 dex in [M/H] and [α/Fe] (505 stars). Panel c) illustrates the values for 1008 stars with errors smaller than 0.15 dex and 0.05 dex, respectively. Finally, panel d) shows all the stars with errors in T_eff lower than 400 K, errors in log  g lower than 0.5 dex and a spectral S/N higher than 15 for the HR10 configuration (1952 stars).