When the amount of compensation in {HEAD ~ 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 {TAIL ~ a predetermined range} 
When the amount of compensation in { HEAD ~ 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 { TAIL ~ a predetermined range }
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD 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 TAIL TAIL TAIL TAIL TAIL TAIL TAIL