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