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