[Lazlo in PA]

Happened to me once when the fuel sender busted on my old 1988 Grand Wagoneer.

LOL. There is a maroon one sitting in my driveway as I write this. It hasn't told me the correct fuel reading in a year. A couple of my collector cars are the same way. I'm just too lazy to drop the tanks to fix them. I just make sure I fill up whenever I go for any distance.

[Paladin2]

I've seen People do dead reckoning by keeping a piece of paper on the dash with the mileage and amount of the last add to the tank.

With an FSJ it's around 10 mpg so the calculations are trivial.