associating a cause of {HEAD ~ said variation} based upon a comparison of said one of said measured characteristics to measured characteristics associated with {TAIL ~ the remaining processing regions} of said subset 
associating a cause of { HEAD ~ said variation } based upon a comparison of said one of said measured characteristics to measured characteristics associated with { TAIL ~ the remaining processing regions } of said subset
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH