I keep accurate fuel records on every car I own. So far this 545 SMG is running exactly .5 mpg behind the 540-6 - 21.72/22.22 for accumulated mileage at around 6,000. It seems worse because the current tank is sitting at 16.2 by the OBC.

The OBC has an average of 22.55 so far for the 545. I did not keep the OBC comparison for the 540-6, but know that it had more OBC error. To keep an accurate OBC comparison, I always zero it after topping off and before cranking. All engine revolutions count, right?