The periods or, equivalently, frequencies of the divided CO signal and the divided reference signal are compared, and {TAIL ~ the result} is used to select {HEAD ~ an appropriate tuning curve} for the CO 
The periods or , equivalently , frequencies of the divided CO signal and the divided reference signal are compared , and { TAIL ~ the result } is used to select { HEAD ~ an appropriate tuning curve } for the CO
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH