As Fig. 4 but showing a DSEP isochrone including heavy-element diffusion and turbulent mixing. In the middle panel the surface [Fe/H] values are shown at selected positions along the isochrone. Each star symbol marks the mean V-band magnitude of the stars in a spectroscopic investigation. The corresponding numbers are the measured [Fe/H] and the number of stars used. In order of increasing V-magnitude, the measurements are those of Origlia et al. (2006), Carraro et al. (2006), Gratton et al. (2006), Peterson & Green (1998) plus the present paper, Boesgaard et al. (2009), and Paper I. In the right panel the change from initial to present surface [Fe/H] is shown at selected positions along the isochrone.