[wagonman76]

I calibrate mine from one fillup to the next using the trip odometer. All it takes is once or maybe twice. After that it is dead nuts within .1 miles over 400+ miles, every time. I prefer to keep mine set to the odometer.

As far as real distance, I don't go by mile markers because I have checked some before and found them to vary a bit. Also the only mile markers are on the freeway which not everyone has near them.

What might be a better way to calibrate to real distance is next time you go a considerable distance, check your exact trip according to Yahoo maps or something like that, then see how that compares.