I have built a simple spreadsheet designed to track the difference between what the MFD displays for fuel mileage and what actual calculated fuel mileage is, on a tank-by-tank and cumulative basis. It has several of my own entries so you can see it "in action." It might be especially helpful for the newbies who are confused by substantial one-tank differences between the display and calculated figures. You will see a column labeled "weighted difference." This is to adjust for tank-to-differences in total miles driven before figuring the cumulative difference. Columns F & G contain formulas, so with a new row you'll need to drag the formula down from the previous row to update the results in those columns and the cumulative difference. Spreadsheet gurus, if you see any flaws in my formulas, please let me know. Enjoy!