I pulled the sending unit and filled the tank half way with gas then bent the float till I got the half tank reading. When mine reads full, it's full. When it reads empty, it's empty. It took a couple of minutes to do. Like was said earlier, due to the shape of the tank, the top half of the tank holds more then the bottom half.
I never let mine get much below half. With the shape of the tank and the fuel pickup, the gas sloshes to the back of the tank under hard acceleration and the fuel pump will suck air. Not a cool sight to have your car die after blowing by someone!!
Scott