Ernie,
There is no way to accurately stick a skymaster. The slightest uneveness in the parking area will make one take seem full and the other 40 gallons low. There are only two times when you know how much fuel is in your tanks, full and empty. As you recommend, get a fuel totalizer and calibrate it over several flights and you will be as close to accurate as you will ever get.
Ed Coffman
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No2 Vaporizer