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