The [α/Fe] vs. [Fe/H] diagram of the APOGEE DR10 high-quality giant sample (Anders et al. 2014; grey dots) in the range 7 kpc <R_Gal< 9 kpc. Overplotted with colours are the thin- and thick-disc chemical-evolution models of Chiappini (2009): the solid lines correspond to the chemical tracks of the thin disc at different Galactocentric annuli (from left to right: 18 kpc, 16 kpc, 14 kpc, 12 kpc, 10 kpc, 8 kpc, 6 kpc, 4 kpc). The colours indicate the age (or look-back time), as indicated in the top panel. The dashed line represents a thick-disc model (for R_Gal = 6 kpc − the Galactocentric dependency for the thick-disc models computed in Chiappini (2009) are minor − see text for more details).