Eric, again let me emphasize that the database does not round actual values - only the display. You're also assuming that everyone inputs miles and gallons. In reality, I believe most input miles and miles per gallon. That's also the way the database was initially created. Miles per gallon by the display is always [that I know of] provided to the tenths. Tenths, then, is what we must assume tank decimals to be.

The reason why I don't calculate cars by miles/gallons is because miles and miles per gallon are the values stored for the reason stated above. It doesn't make a mathematical difference, as nothing the user inputs is ever rounded.

There is also the additional error of the car's display value and/or the gas pump's inaccuracies. These can only be assumed and estimated. So, when calculating error, one would have to find the error for each car (somehow) and then incorporate that into the error for each model. I have no idea how that could be achieved, but then again I just took my first statistics course this year.

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