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