[Fat Charlie]

You don't need to go close to empty, it's just the fastest way to get the most accurate calibration. Longer distances beteen inputs make for more accurate results, just like a 36" level is more reliable than one on a keychain, and a 72" level is even better.

You won't get accurate "per shift" data until you're calibrated. If you admit that and go deeper into your tank a few times to get it calibrated, you'll start getting accurate numbers, which will pay off in more ways than simple shift data: a well calibrated gauge will teach you more about your car than a generic "keep my foot on the accelerator as little possible" rule. There's a time and a place for everything, and your car, tires and feet are different from other cars, tires and feet. Once you're calibrated, go ahead and reset the long trip after every shift. Have fun!

But the short trip numbers will teach you more about how to get the most out of your car than any list of short fills can ever hope to.