{HEAD ~ The eye position detector} monitors {TAIL ~ light} reflected from the users eye to identify the pupil position 
monitors
{ HEAD ~ The eye position detector } monitors { TAIL ~ light } reflected from the users eye to identify the pupil position
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH