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