Gotcha. You may still be able to make it more accurate. I think the top to bottom on an AD Fuel tank is about 12 inches. Adjust the arm so that when the lever arm sweep is exactly halfway between full and empty, that the float is 6 inches down from the top of the tank ( or whatever you determine the middle of the tank is.
That way, even if the travel isn't all the way full or all the way empty, you'll at least know that the halfway mark is exactly 9 gallons.
