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