Conventional value of the result of weighing in air, in accordance with OIML D 28 Conventional value of the result of weighing in air [3]. For a weight taken at a reference temperature (tref) of 20 °C, the conventional mass is the mass of a reference weight of a density (rref) of 8 000 kg m–3 which it balances in air of a reference density (r0) of 1.2 kg m–3