If light from the image source becomes misaligned with respect to the pupil, a physical positioning mechanism adjusts {TAIL ~ the relative positions} of the image source and the beam combiner so that {HEAD ~ light} from the image source is translated relative to the pupil, thereby realigning the display to the pupil 
If light from the image source becomes misaligned with respect to the pupil , a physical positioning mechanism adjusts { TAIL ~ the relative positions } of the image source and the beam combiner so that { HEAD ~ light } from the image source is translated relative to the pupil , thereby realigning the display to the pupil
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH