I usually hit FULL when I fill the tanks, and after consuming say 100 liters, I add 35 at the pump, I do the ADD plus number of liters added. Even after several of these partial full cycles, on the next fillup at the pump I am rarely more than a few liters off.
After nearly 18 years of good service my EDM700 is now shipped back from JPI after installation of new display. The old one was fading.