Top: linearity check of the photometric conversion to r_instr. of pointing 7 through its overlapping regions with the rest of the mosaic. Bottom: linearity check of the photometric calibration with SDSS, in this case for pointings from the mosaic in g band. The stars used for the linear fitting are shown as black dots, and are the majority of those having g_SDSS ≲ 20.5, while the stars not used are shown as red dots (outliers or those with errors larger than 0.03 mag). In both panels the white squares give the median values in 0.25 mag-wide bins and the black line shows the one-to-one relation.