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