{HEAD ~ 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 {TAIL ~ width}, of the light beam directed between the reflecting surfaces 
{ HEAD ~ 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 { TAIL ~ width } , of the light beam directed between the reflecting surfaces
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 TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH