The detectors are positioned to provide {HEAD ~ a first pair} of {TAIL ~ output signals} in phase quadrature and representative of the interference fringe pattern inpinging thereon 
of
The detectors are positioned to provide { HEAD ~ a first pair } of { TAIL ~ output signals } in phase quadrature and representative of the interference fringe pattern inpinging thereon
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH