The signal variations provide {TAIL ~ step count signals}, and the step count signals are compared to {HEAD ~ the command pulses} to detect a disparity 
The signal variations provide { TAIL ~ step count signals } , and the step count signals are compared to { HEAD ~ the command pulses } to detect a disparity
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH