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