These sides permit total internal reflection, when properly angled, so that the height of the line produced on the document is less than the o diameter, or width, of {HEAD ~ the light beam} directed between {TAIL ~ the reflecting surfaces} 
directed between
These sides permit total internal reflection , when properly angled , so that the height of the line produced on the document is less than the o diameter , or width , of { HEAD ~ the light beam } directed between { TAIL ~ the reflecting surfaces }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH 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 TAIL