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