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