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Mass Standard



The unit of mass represented by the International Prototype Kilogram, consists of a cylinder whose height and diameter are both 39 mm and is made of 90% platinum and 10% iridium.
The Japanese standard mass, the Japanese Prototype Kilogram, is made exactly in the same shape and of the same material as the International Prototype Kilogram, and is kept at NRLM.

Kilogram Prototype

The mass of the Japanese prototype kilogram is compared for consistency every thirty years with the international prototype kilogram kept at the International Bureau of Weights and Measures in France.


Kilogram Prototype

Precision Improvement

NRLM has developed built-in balance counter-weights (sinkers) of different volumes and surface areas. Using these counter-weights to correct air buoyancy and absorb gas molecules on their surface, was first developed at NRLM. Standard mass was verified to an accuracy of 10 -9 employing the above technology.


Sinker System for Correction of Air Buoyancy

Balance of the Prototype Kilogram

NRLM has developed balance which can be broken down to 0.1(g (10 -10) per kilogram.


Balance of the Prototype Kilogram



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