Scangauge Offset Factor for MPG?

[pumpkin]

I have taken two long trips and carefully measured the mpg. Based on odo, I got 30 mpg, while the scangauge showed an optimistic 33 mpg. Has anyone else noticed this? Did you put in a correction factor? I'm going to try about 9%to try to make them agree. Have you found this necessary? Did you get similar factor value?
JD

[Tom @ Fast Forward]

I have used the ScanGauge for the instant mileage (kind of fun to see MPG going downhill :)) but not for long term MPG.

[Mark]

If you have access to a GPSr, you may want to also check that your odometer is reading correctly before determining a correction factor...

[maggie]

I have found the Scangauge to be very accurate in gauging fuel economy and is within about two percent. I found my odometer to be off by a few percent also. Like Mark said, start with the GPS.