The optical encoder 1, wherein the set of {TAIL ~ at least four light sources} comprises {HEAD ~ eight light sources} 
The optical encoder 1 , wherein the set of { TAIL ~ at least four light sources } comprises { HEAD ~ eight light sources }
OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD