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