In addition, a subtractor produces {HEAD ~ an error signal} by subtracting {TAIL ~ the output signal} from the reference input signal 
In addition , a subtractor produces { HEAD ~ an error signal } by subtracting { TAIL ~ the output signal } from the reference input signal
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH