The impedance across {HEAD ~ the first and second devices} is compared to provide {TAIL ~ the respective bit} of the corresponding digital output word 
The impedance across { HEAD ~ the first and second devices } is compared to provide { TAIL ~ the respective bit } of the corresponding digital output word
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH