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.
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.