MPG Readers, are they accurate?

[DJLapri]

I have an MPG reader by KIWI and I use an FS2 also. If an engine is burning HHO and gas, the mpg reader really has no idea how much gas is being burned, rigth? Its early so maybe I am not thinking logical at the moment. Am I incorrect?

[mgen100]

You know just check how many miles you go on a tank of gas thats what i do cause the computer does not seem to ajust for the HHO accurately.