The graph of FIG 4 represents {HEAD ~ magnitude values} of the output of the analog to digital converter 44 as {TAIL ~ the media} 12 is transported in the longitudinal direction from its initial starting point 
The graph of FIG 4 represents { HEAD ~ magnitude values } of the output of the analog to digital converter 44 as { TAIL ~ the media } 12 is transported in the longitudinal direction from its initial starting point
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH