One big problem is, that in SI base unit for mass is kilogram not gram.
This is definitely not a "big problem". There is nothing that sets apart the "base" units in my old library from any other units, except for the fact that they happen to be defined using baseUnit!(), not by adding a prefix. Kilogram just happens to be defined as kilo!gram so that you don't get things like millikilogram.
— David
