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