The four boxes show the counts in the raw frames of the modulation demodulation efficiency calibrations
for 
<ul>
<li>both detectors (CAM1 and CAM2) and 
<li>both readmodes (S= SlowPolarimetry and F=FastPolarimetry).
</ul>
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The counts in the raw frames are composed of a bias level of ~1000 ADU
plus lamp flux.  For every raw frame, the counts are taken in one even row
(pixel area = [60 268 260 268]) and in one odd row (pixel area = [60 269
260 269]).  The average over all raw frame planes of the cube is taken,
resulting in a mean odd_row and a mean even_row counts for both detectors.
The maximum between the even_row and odd_row values is taken, for both
cameras separately.  The maximum over all raw frames is taken. This QC
parameter is used to check for saturation and under-illumination.