Could one just drain all useable fuel and then add fuel one gallon each side, so two gallons at a time, and mark a wooden stick in one gallon increments? I would think this should work with the airplane sitting in a wings level position. If one gallon is added in each tank and a few moments allowed to self level, it should be very accurate. You could close the fuel valve to stop the tanks from feeding each other and the fuel self leveling, throwing off the readings. Then just fill one tank and take the measurements. But, it might be more accurate, no chance of fuel valve allowing some internal leakage, if each tank was filled one gallon at a time and they self level through the fuel valve.
Am I missing something that would make this idea not work?
