The Elemental Unit measures elemental flow rates and elemental fractions of specified elements in the mixture.
For each of the compounds, the chemical formula must be known and correcly parsed. Chemical formula is automatically obtained from the simulation environment, if available.
Elemental mass flow rates use the atomic masses as given by "Atomic weights of the elements 2009 (IUPAC Technical Report)", M.E. Wieser and T.B. Coplen, Pure Appl. Chem., ASAP Article, doi:10.1351/PAC-REP-10-09-14.
For consistency, elemental mass fraction uses the ratio of the atomic mass and the total atomic mass calculated from the same source, over all elements in the mixture. The molecular weights of the compounds as exposed by the simulation environment are not used.