An initial interferometric position measurement of the stage is averaged with at least one additional measurement corresponding to {HEAD ~ a displacement} of the stage from {TAIL ~ its initial position} 
from
An initial interferometric position measurement of the stage is averaged with at least one additional measurement corresponding to { HEAD ~ a displacement } of the stage from { TAIL ~ its initial position }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL