{HEAD ~ 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 {TAIL ~ a function generator} to thus obtain a square root of the distance 
{ HEAD ~ 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 { TAIL ~ a function generator } to thus obtain a square root of the distance
HEAD HEAD HEAD HEAD HEAD HEAD 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 REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH