The Nightly 2MASS Photometric Zero Point plots show the differences between catalog magnitude and extinction-corrected instrumental magnitude for the standard stars in each calibration scan. This difference is plotted versus the UT of the calibration scan. A number of key calibration evaluation parameters are encoded on the plots, using color and annotations. Calibration set is not used in zero point evaluation.
Night is broken at that point.
Not used in zero point evaluation. Night is broken at that point. The maximum allowable time between calibration observations. For gaps larger than this, the night is broken. Note that this parameter can be over-riden during Science QA review.