Correction of the systematic errors in G. The horizontal axis is the observed (uncorrected) G magnitude and the vertical axis is the difference between that value and the synthetic G magnitude assuming the G sensitivity curve in this paper and a ZP of 0. The points with error bars show the data, color-coded according to data set, and the dark green solid line shows the fit used to derive the correction proposed in this paper. The size of the error bars is explained in Sect. 4.