means for sensing {HEAD ~ a start} of {TAIL ~ a line image} to generate said clear signal; and 
of
means for sensing { HEAD ~ a start } of { TAIL ~ a line image } to generate said clear signal ; and
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH