These sides permit {TAIL ~ total internal reflection}, when properly angled, so that {HEAD ~ 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 
These sides permit { TAIL ~ total internal reflection } , when properly angled , so that { HEAD ~ 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
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH 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