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