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