The apparatus comprises {HEAD ~ a combination} of {TAIL ~ sum} and differencing amplifiers which combine detected signals into a form which can be used to compute the angle and magnitude of displacement 
of
The apparatus comprises { HEAD ~ a combination } of { TAIL ~ sum } and differencing amplifiers which combine detected signals into a form which can be used to compute the angle and magnitude of displacement
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH