national measurement act 1960 determination by the national standards commission Recognized-Value Standard of Measurement of Density Standard Mean Ocean Water In pursuance of paragraph 8A(1)(a) of the National Measurement Act 1960, the National Standards Commission hereby determines that the magnitude of the density of standard mean ocean water at a temperature of 3.99°C and at a mean pressure of 101 325 Pa shall be a recognised-value standard of measurement having the exact value 999.975 kg.m-3. For the purposes of this Determination standard mean ocean water is pure water, free of dissolved gas, in which the ratio of the number of oxygen atoms of mass number 18 to the number of oxygen atoms of mass number 16 is 0.002 005 and the ratio of the number of deuterium atoms to the number of hydrogen atoms is 0.000 155 76. Dated this 21st day of March 1985 The common seal of the national T.J. PETRY standards commission was hereto affixed by authority of the Commission in the presence of