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