Difference in the photometry between the CASU default reduction and the 2MASS catalog. The blue, green, and red data points show the J, H, and K_S bands, respectively. The color shading represents source density in a 0.2 × 0.05 box in the given parameter space and the gray solid line a running median along the abscissa with a box width of 0.5 mag. Several processing steps contribute to the apparent offsets, which are all avoided in our data reduction.