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