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