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