The scangauge isn't driving the car, you are. On one hand you have your "butt dyno" and anticipation. On the other hand you have your "butt dyno", anticipation AND a scangauge. I wouldn't hesitate to be on the other side of your wager as long as your "butt dyno" isn't better than my "butt dyno".
I'll bet my butt dyno can whup your butt dyno! LOL! LOL!
I bought my car (34/40) expecting to get an average of 35mpg, so i should be happy with my average of 40mpg. But it seems like i REALLY REALLY tried to incorporate changes to my driving technique... and it payed off, but only slightly.
normal driving when i got the car got me about 39mpg. My last fill up was 41.2mpg.
guess i should break down & get a scanguage as my next step?