> Yeah. I did not find the Units in opm-parser. I will use this one.

basically the only reason why you didn't find them in opm-parser is that this would lead to a circular dependency: these units are in opm-core and opm-core uses opm-parser, so opm-parser cannot use anything which is in opm-core and thus has to roll its own unit framework as a consequence. In the long run, we should probably think about splitting opm-core into "basic stuff which does not depend on {opm,dune}-*" and "basic stuff which can be used to build a simulator". This way, the parser could depend on the former and the latter could depend on the parser.