Left panel: distribution of the reference stellar parameters in the T_eff and log g plane for the ELODIE library (solid points), the benchmark stars (crosses), and the S4N stars (triangles). Right panel: as before but with the stellar parameters derived by SP_Ace. The colors code the [Fe/H]. Errorbars are reported in light gray. The solid, dashed, and dotted black lines trace the isochrones for [M/H] = 0.0 dex and 5 Gyr, [M/H] = −1.0 dex and 10 Gyr, and [M/H] = −2.0 dex and 10 Gyr, respectively.