This plot monitors the persistence in both <b>IFS dark</b> and <b>IFS background</b> calibrations 
which can be generated by previously acquired IFS optical distortion calibrations.
These optical distortion calibrations can leave a pinhole slice pattern in the IFS dark or background pipeline product. 
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The QC parameter is simply: the median counts in the pipeline product in a window P = [770, 1300 --- 850, 1440] 
minus the median counts in window B = [640, 1470 --- 720, 1570].
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Window P (pinhole) is the area where the pinhole slice pattern can show up and window B (background) is the area 
off the pinhole slice pattern areas on the detector. 

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This kind of monitoring was introduced 2018-01-01.</font><p><font size="2">
IFS_DARK master frames are not used to calibrate observations, only
the ancillary IFS_DARK product IFS_STATIC_BADPIXEL is used. IFS_BACK
calibrations are used to calibrate science observations.  


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Since the
background level of the IFS_BACK calibration depends on the exposure
time (DET.SEQ1.DIT) and the ambient temperature, template subtraction
(subtraction of a reference product with the same DIT and ambient
temperature) might give persistence values with samller error bars.
However the two analysis windows P and B are close to each other,
and measure the values at the identicat DIT and ambient temperature. 
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