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