I know this is somewhat petty, but yet I see each time when I fuel-up that Fuelly is changing the accuracy of the number of KM which I enter, and not in a way which makes any sense to me. (i.e. I entered 273.7 which have been changed into 273.749).
That also happens if I edit the fuel-up input on-site.
I think it is because the fuelly code is written in miles and gallons, so it converts your km into miles and your liters into gallons, then converts back to liters/km, and the extra digits are from rounding error.