Perhaps a check, something like "I see you're using US Gallons but are calculating MPG the UK way. Do you want to change that? [Yes, take me there] [No, I like to have confusing metrics] "

It was my logic that was in error. I needed to take the Travelled value (in Miles) and divide it by the CURRENT Fillup value (in US Gallons) to get Miles/Gallon ("my MPG").

Our numbers don't perfectly match, but of the 11 items in the example, we're off by an average of 0.01. Close enough for me. :)

Thanks for helping with this! Love to see developers who actually talk to their customers.

That was it. I was certain I'd set fuel units to Gallons (US) and Consumption to mpg (us), but it wasn't. It was set to mpg (uk). As soon as I made the change, the numbers look "better".