When the amount of {HEAD ~ compensation} in {TAIL ~ the fine displacing drive unit} exceeds a predetermined value, the Y axis drive system is actuated so that the amount of compensation by the fine displacing drive unit lies within a predetermined range 
When the amount of { HEAD ~ compensation } in { TAIL ~ the fine displacing drive unit } exceeds a predetermined value , the Y axis drive system is actuated so that the amount of compensation by the fine displacing drive unit lies within a predetermined range
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH