Fuel Gauge reads erratically?

It reads, but with varying accuracy across its range. I'd like to know how to rebuild it, so it reads uniformly, or with a determinable inaccuracy. I have electronics knowledge but haven't been able to figure this out. This is my 7th Square body; I've been rebuilding old vehicles since I was 13. I have a 78 Scottsdale with the same engine and drive train and the same problem. I think after 6 years, I've invested enough time trying various things that were Addisonian experiments. Now it's your turn. Thanks!