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