I just calibrated mine today. The process is easy and simple. Get the tanks as low as possible and then mark off every 5 gallons. The math came out PERFECT. Brimmed tanks came out to exactly my useable fuel capacity to within 0.2 gal +/-. I am extremely pleased with it and takes the guesswork out of filling the tanks. Also helps keep accurate burn rates for those of us without expensive engine monitors!

Been using this guy for several years now on my warbird. Have found it well-designed and durable, and Im about to get a second one for backup. When you stick your tanks before departure, it really doesnt matter how well the gauges work!