The system 3, wherein {HEAD ~ the average position} is linearly proportional to the average of the measured phases corresponding to {TAIL ~ the multiple positions} 
The system 3 , wherein { HEAD ~ the average position } is linearly proportional to the average of the measured phases corresponding to { TAIL ~ the multiple positions }
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL