I estimate that the information display mpg is off optimistically by around 7.5%. Comes out real close when I do the math.

To eyeball that, if the display says 44 mpg (for example), I multiply (in my mind) 44 by 7, and get 28X (two hundred eighty something) or 29X (two hundred ninety something). It's actually 30X (three hundred something, but I'm conveying what I quickly "estimate." Then I know to pull about 3 mpg (29X, move the decimal 2 places to the left = 2.9X ... so more or less 3) off the 44 mpg on the display, and effectively I got about 41 mpg. I eyeball that, like that, then actually do the math on miles per gallon filled. Comes out very close eyeballing it like that.