The frequency of the back EMF signal is determined from {HEAD ~ the zero crossings} of {TAIL ~ the EMF signal} 
of
The frequency of the back EMF signal is determined from { HEAD ~ the zero crossings } of { TAIL ~ the EMF signal }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL