U_RGO − g vs. g − r diagram for the regions 80° < l <  85° (top) and 185° < l <  190° (bottom). The density of sources is portrayed by the contoured colour scale. Sources with g <  20 and errBits = 0 are included. The solid line in red in both is the unreddened main sequence, while the dashed line is the reddening line for an F5V star extended up to A_V = 10. The blue line represents the giants. Numerical detail on the tracks is provided in Appendix D. Top panel: example of a region in which the pipeline calibration has produced a uniform outcome, lower panel: instance of where it is clear that there is some variation in the U_RGO photometric scale.