. . . "Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material." . "http://en.wikipedia.org/wiki/Relative_density"^^ . "d" . "http://www.iso.org/iso/catalogue_detail?csnumber=31889"^^ . "Relative Mass Density"@en . . "\\(d = \\frac{\\rho}{\\rho_0}\\), where \\(\\rho\\) is mass density of a substance and \\(\\rho_0\\) is the mass density of a reference substance under conditions that should be specified for both substances."^^ .