Magnitude differences measured for objects found in the overlapping pointings using a fixed aperture of 6 arcsec in the r band (rSDSS). Each point corresponds to a point source in one of the overlapping areas (distinguished here by the colors). The light symbols are the magnitude differences before correcting for the PSF of each tile, and the heavy symbols are the magnitude differences after that correction is applied. The error bars are those of the individual tiles, added in quadrature.