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