The improvement 11 wherein said detecting {HEAD ~ means} includes {TAIL ~ means} for detecting the longitudinal position of said beam spot on said second scan path 
includes
The improvement 11 wherein said detecting { HEAD ~ means } includes { TAIL ~ means } for detecting the longitudinal position of said beam spot on said second scan path
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH