History of balances and of weights
SP is designated as National Laboratory for Mass by the Swedish Government according to the Act (1992:1119) and the Decree (1993:1065) concerning testing and metrology.
National Laboratory for Mass
As National Laboratory we have the best resources and the best competence in our country and the Mass Section is in charge of the ‘National Kilogram’. This means that we have in our hands the entire chain of traceability required by modern quality systems for the calibration of weights and weighing instruments.
Research and development
The National Laboratory for Mass is a part of the Swedish National Centre of Metrology. To maintain and develop our high competence we take part in R&D-projects related to weighing technology.
Member of CCM
Being one of the world's most experts in the field of mass, SP is a member of CCM, the Consultative Committee for Mass and Related Quantities (Comité Consultatif pour la Masse et les grandeurs apparentées).
Kilogram prototype
Since 1889 the SI unit kg is defined as being the mass of the international kilogram prototype in Sèvres. In Sweden the unit of mass is maintained as the ‘National Kilogram’. It was produced together with the international prototype, and is like this consisting of 90% platinum and 10% iridium.
A century of safe-keeping
At the last major international calibration of national kilogram prototypes in 1991, the mass of the Swedish prototype was found to be 0,999999965 kg, with an uncertainty of measurement of ±2,3 µg (k=1).
It was noted that, after a whole century, the mass of the Swedish National Kilogram had changed by only 2 µg relative to that of the international prototype. No other country in the world had looked after its kilogram better!
History of balances and of weights
To perform the finest weighing, of course we use our finest balance, but this balance has not always been the same. We are pleased to tell a little more about the three generations of primary balances.
They have been:
- The Rueprecht balance 1893–1977
- The Voland balance 1977–1991
- Tha Sartorius balance 1991–
During the years several for Sweden important weight comparisons have been performed. Old reports can be downloaded in the meny to the right (Swedish only).