I got a weird MPG spike. I average 24 MPG, but after a fuel up last week I got a spike up to 28, now it's back to 24. I just can't figure it out... all my odometer and fuel up data is correct, but the calculation is way off. I even tried adjusting some of the numbers a bit hoping maybe it would re-calculate, but it still stays up around 28.
That sort of error usually corrects itself on the next fuelup, when the mpg looks unusually low. That's also the reason you should use several fuel fills instead of only one to get a truer fuel consumption.