Aircraft Fuel-Finger fuel gauge specially designed for Cessna 172 Skyhawk with standard 75 liters tank.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.Made of heavy, clear plastic and easy to use. Simply insert fuel gauge until 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.