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