These frames are taken approximately once per month, as a set of 3 consecutive exposures of 3600 secs each. These data are de-biased and combined into a MASTER_DARK, in which the average dark level is measured (in ADU/px/hr).
Box 1 has the DARK current, in ADU/hr/pix. For the new CCD, it is measured across the whole chip. The old CCD (used until 2008-03) had a significant glow, and the DARK current was measured outside the glow, in a box extending up to row @3800. Box 2 is displayed in history plots up to 2008. It measures the glow itself. Note that there was no glow between 2003-07 and 2004-07-26.
Corresponding data from the GIRAFFE master calibration (re)processing project are available for the first two years and are marked separately.
Find more information about GIRAFFE DARK frames here.
Other QC parameters related to detector properties (like contamination, linearity, gain) are trended in the same group.