  We summarize the Sloan Digital Sky Survey data acquisition and processing
steps, and describe runQA, a pipeline designed for automated data quality
assessment. In particular, we show how the position of the stellar locus in
color-color diagrams can be used to estimate the accuracy of photometric
zeropoint calibration to better than 0.01 mag in 0.03 deg2 patches. Using this
method, we estimate that typical photometric zeropoint calibration errors for
SDSS imaging data are not larger than ~0.01 mag in the g, r, and i bands, 0.02
mag in the z band, and 0.03 mag in the u band (root-mean-scatter for zeropoint
offsets).
