If desired, {TAIL ~ the scan logic} 20 may then compute from the error signal {HEAD ~ the current position} of the media 12 
If desired , { TAIL ~ the scan logic } 20 may then compute from the error signal { HEAD ~ the current position } of the media 12
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH