a first rotatable means for controlling the horizontal movement of {HEAD ~ said cover} through {TAIL ~ Said linear means}, 
a first rotatable means for controlling the horizontal movement of { HEAD ~ said cover } through { TAIL ~ Said linear means } ,
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH