In my 95, the gauge was showing 1/4 tank less then what was in there. So If I filled it all the way up, it would show being 3/4 filled. After calculating my mileage after a couple of tanks, I determined I could get at least 250 miles out of it. However the gauge shows empty at 170 miles. So I drove well into the E and then filled it up. When I did that it was only wrong by 1/8th of a tank when full. Now when full it shows 7/8ths or so. Almost to the Full mark.
So I believe if you need to calibrate it, you have to run it till empty, or fumes, then fill it all the way up.