Gas gauge not working? I think I fixed it.

If you have an adjustable power supply 0-5V, apply directly it to the gauge meter. Start with low voltage. Find the voltage for empty, and full. I would think there needs to be a span of a half volt to have resolution. So for example empty is 3.5 and full is 4.0 the cal unit will work.

If you provide voltages and sender resistance values empty/full resistance values, I could hard code calibration. By doing that, circuit would be simpler to make. No buttons, and a few less parts. It will work only for your situation.