I calculated by calculating how much gas I put in the tank and dividing the number of miles. Yeah, that number that displays is really off. It showed I was getting around 24 on the highway when I drove to Orlando from Atlanta. I knew it was way off so I reset it and it went to 21 for the rest of the trip. Now I do think the remaining gallons is fairly accurate. I did use that while driving around and it seemed to be close.
Scott