[COcyclist]

I "re-calibrate" the ScanGuage II at every fill-up. I find it varies a few percent each time but the larger the fill-up the more accurate it is. I use the red button, MORE, FILLUP etc. and SAVE when done. I don't consider ScanGuage mpg values to be absolutely accurate but the instant feedback is very useful.

I use:
MPG WT
LOD MAP

The Scanguage temperature readings are much more accurate than the factory temp guages as they have been "idiot lighted" in many modern cars (important when grill blocking). I use the MAP setting to monitor boost in my turbo car and I will cycle through and monitor intake air temps too.

I find the CURRENT and TODAY trip mpg TRIP readings useful as well.