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