The numbers are from the on-board computer. Don't know how accurate it is, but it's one measure that I'm assuming is somewhat consistent since every EX has it built-in.

I will track a couple of tankfuls manually later on and compare the results with that shown by the EX's computer. I would think though there's enough variation in where different gas pumps "click off" that it's not easy to be tightly accurate, even computing it manually.