During periodic calibration, sampling {HEAD ~ the output} of {TAIL ~ dark reference cells} on a CCD nets an initial D.C. restoration voltage level 
of
During periodic calibration , sampling { HEAD ~ the output } of { TAIL ~ dark reference cells } on a CCD nets an initial D.C. restoration voltage level
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH