Displacing {HEAD ~ a portion} of {TAIL ~ the YZ movement line} allows vertical displacement of the platform to be traversed 
Displacing { HEAD ~ a portion } of { TAIL ~ the YZ movement line } allows vertical displacement of the platform to be traversed
OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH