There is a toothed platen for locating the forcer so that {HEAD ~ the forcer} is movable over {TAIL ~ the platen} 
is movable over
There is a toothed platen for locating the forcer so that { HEAD ~ the forcer } is movable over { TAIL ~ the platen }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL