Jason
I was wondering if you have considered adding functionality to the database to track manual mpg calcs vs the nav computer mpg, since you already have the facility for either man. or computer. Why not both? For example, on the page that shows a vehicle tank history, the plot at the top shows the mpg over time. If you added an additional symbol to the plot, you could show how spot on, or how off the manual and computer mpg calcs are. I added an additional vehicle to track my computer readings (I use man. mpg calcs), but then I realized I couldn't compare them easily

, and I would invalidate the avg mpg for all vehicles of the type I drive.
