The current is then measured between the electrodes at the plurality of voltages and {HEAD ~ a contamination level} is determined using {TAIL ~ the measured currents} 
is determined using
The current is then measured between the electrodes at the plurality of voltages and { HEAD ~ a contamination level } is determined using { TAIL ~ the measured currents }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL