{TAIL ~ These sides} permit {HEAD ~ 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 the light beam directed between the reflecting surfaces 
{ TAIL ~ These sides } permit { HEAD ~ 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 the light beam directed between the reflecting surfaces
TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD 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 OTH OTH