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