Good catch and no, the usual is not 3.7 mpg difference between displayed and calculated. Over the life of the car the average is 1.93 mpg difference or only 3.87% error. One time it was 0.1 and 0.4 and another was 8.2 mpg difference. The ones with the largest error there was when the car was nearly out of gas and limped for a mile on battery alone and no fuel and the display was 45.1 mpg but calculated as 53.3 mpg. Neat to learn little things like that sometimes.

And I prefer the side streets rather than open highway however 90% of my day is probably on the Interstates (or Freeways to you left-coasters). I also like the warmer temps. My rough guess at temperature-per-tank average is 51 degrees for those 14 tanks (only started noting temps at the beginning of October instead of August). Garsh I like all of the number-crunching I can do with this car. So much of a game every day.

--> Averaged 685 miles/week and 49.0 mpg in first year (35.7k miles from Aug 7, 2006 to Aug 7, 2007)