A measuring unit measures {HEAD ~ the tool position} with {TAIL ~ an accuracy} higher than that to which the first drive unit can respond 
A measuring unit measures { HEAD ~ the tool position } with { TAIL ~ an accuracy } higher than that to which the first drive unit can respond
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH