a displacement/drive mechanism for driving {HEAD ~ the pickup base} in {TAIL ~ a radial direction} of the optical disc; wherein 
in
a displacement / drive mechanism for driving { HEAD ~ the pickup base } in { TAIL ~ a radial direction } of the optical disc ; wherein
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH