I did technique like Mr Kite, and found I drove about 3% further than odo. However its 6 months and 17k miles later, tires should have worn slightly and I probably need to check calibration again.

I have seen the cars estimated MPG be off in either direction. Seems to depend on driving techniques used. As my mileage has gotten more extreme, the car underestimates more and more. When I first started it tended to overestimate.

Somewhat related, the low gas light comes on way too soon. I'm figuring about 3 to 3.5 gallons left. That would make since to come on that soon in a 15mpg car, but at 25/35mpg, it really could wait a while longer. I'm very sad I don't have an estimated-miles-remaining. I think its availabe on the cars with nav. Is it accurate or does it show zero miles too soon?