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