. . . . . . . . "M_r" . . . "Relative Molecular Mass"@en . "http://en.wikipedia.org/wiki/Molecular_mass#Relative_molecular_mass"^^ . "\"Relative Molecular Mass \" is equivalent to the numerical value of the molecular mass expressed in unified atomic mass units. The molecular mass (m) is the mass of a molecule." . "http://www.iso.org/iso/catalogue_detail?csnumber=31894"^^ . . . . . .