Voltage outputs 78 and 80 from outputs 68 and 70 are input into a subtracter circuit 84 which provides an output 86 that is {HEAD ~ the difference} between {TAIL ~ voltage outputs} 78 and 80 
Voltage outputs 78 and 80 from outputs 68 and 70 are input into a subtracter circuit 84 which provides an output 86 that is { HEAD ~ the difference } between { TAIL ~ voltage outputs } 78 and 80
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH