maintaining {HEAD ~ constant tension} over {TAIL ~ the length} of each web as the webs travel over the support surface 
maintaining { HEAD ~ constant tension } over { TAIL ~ the length } of each web as the webs travel over the support surface
OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH