Then, {TAIL ~ the pseudo tracking servo output signal} is used to compute {HEAD ~ the speed} of the sledge motor 
Then , { TAIL ~ the pseudo tracking servo output signal } is used to compute { HEAD ~ the speed } of the sledge motor
OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH