{HEAD ~ A pair} of {TAIL ~ photodetector output signals} are positioned so as to be responsive to the interference pattern produced by the pair of laser beams of the ring laser 
{ HEAD ~ A pair } of { TAIL ~ photodetector output signals } are positioned so as to be responsive to the interference pattern produced by the pair of laser beams of the ring laser
HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH