The two flat mirrors are rotated in synchronism for scanning {HEAD ~ the light beams} longitudinally along {TAIL ~ the document} 
longitudinally along
The two flat mirrors are rotated in synchronism for scanning { HEAD ~ the light beams } longitudinally along { TAIL ~ the document }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL