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