A ratio of IP/IA of the currents flowing in {HEAD ~ the terminals P} and {TAIL ~ A} is detected 
A ratio of IP / IA of the currents flowing in { HEAD ~ the terminals P } and { TAIL ~ A } is detected
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL OTH OTH