PARSEC isochrone for [M/H] = –2.75 and an age of 10.2 Gyr (small black dots) (from Bressan et al. 2012). The red symbol shows the parameters we derived (T_eff from the SDSS photometry and logg from the Fe ionisation equilibrium). The blue symbol on the isochrone corresponds to a log g that is 0.4 dex higher and corresponds to a disagreement in A(Fe) of 0.13 dex between the abundance derived from Fe I lines and that derived from Fe II lines. This value is well within the uncertainties.