determining {HEAD ~ a reference value Ro} relative to an internal resistance Ri of the tank, an upper limit Ro+r and {TAIL ~ a lower limit} 
determining { HEAD ~ a reference value Ro } relative to an internal resistance Ri of the tank , an upper limit Ro+r and { TAIL ~ a lower limit }
OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL