Volkov, first of all welcome to the forum.
If you want to use MPGuino you can use official v0.86 version (sometimes there's a bug in the metric readings), or you can use metric "canadian" version (I'm using it for Berta right now with some custom mods to the code).
So you have at least two options that don't require any mods to the code.
If you have any questions regarding MPGuino installation or code you'll surely find help here.
What kind of car are you driving? Register it into your
Garage with a fuel log.
P.S. I was in Budapest three weeks ago
My company headquarter is located there.