Not sure about calibrating. As far as the rest, I don't think you will ever run a vehicle empty enough to take the full capicity to fill it back up. Meaning, on a 27 gallon tank, it would be very hard to run it low enough to take 27 gallons without leaving yourself dead on the road. There will always be a few gallons in the tank.
i would suggest figuring your mileage by the miles/gallons method and see how far off the trip computer is. I'll post back later if I find out the display cna be calibrated.