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