Standard deviation versus offset (both normalized by their respective step in the model grid) of the difference between the fitted atmospheric parameters in each case (with u′ = u + δu) and the ones fitted when substituting the u-band for u from SDSS. The top panel shows the effects on log ɡ and the lower panel on [Fe/H]. Each point represents a different δu value, indicated on the corresponding label. A value of −0.04 mags is an appropriate correction for u that would put the parameters closer to those fitted using SDSS.