Means are provided for mounting the slotted member upon the substrate and permitting the rectilinear movement thereof in {HEAD ~ a plurality} of {TAIL ~ parallel spaced steps} 
of
Means are provided for mounting the slotted member upon the substrate and permitting the rectilinear movement thereof in { HEAD ~ a plurality } of { TAIL ~ parallel spaced steps }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL