The average position can be used to more accurately determine {TAIL ~ the average position} of an alignment mark on a wafer carried by {HEAD ~ the stage} 
The average position can be used to more accurately determine { TAIL ~ the average position } of an alignment mark on a wafer carried by { HEAD ~ the stage }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD