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