A signal corresponding to a distance from the present position of the laser beam spot to the desired track is obtained from the displacement and a desired count value, and is inputted to {HEAD ~ a function generator} to thus obtain {TAIL ~ a square root} of the distance 
to obtain
A signal corresponding to a distance from the present position of the laser beam spot to the desired track is obtained from the displacement and a desired count value , and is inputted to { HEAD ~ a function generator } to thus obtain { TAIL ~ a square root } of the distance
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH