Universal aircraft fuel gauge.Easy to use, simply insert "Fuel-Finger" until it touches bottom of the tank. Place finger firmly over top opening to lock fuel in tube. Remove to read gallons usable on calibrated scale.Made of heavy, clear plastic and easy to use. Simply insert fuel gauge ntil it touches the bottom of the tank. Then place your finger firmly over the top of the opening to lock fuel in the tube. (For use in both main and auxiliary tanks.)This fuel gauge is ideal for when the pilot must take a less-than-full fuel load due to weight considerations or measuring how much is really in the tank.