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