File:MassStandards 005.jpg

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The platinum-iridium cylinder (right) was the primary standard kilogram for all metric measurements in the U. S. Known as Kilogram No. 20, it was a copy of the International Prototype Kilogram, which was preserved at the International Bureau of Weights and Measures at Sevres, France. Kilogram No. 4 (left, under double bell jar), a duplicate of No. 20, was used as a secondary standard. Noth cylinders were 39 mm in diameter and 39 mm. high; they were made of 90 percent platinum and 10 percent iridium. Re-comparison of Kilogram No. 20 with the international standard in 1937 showed that the United States standard had changed by only one part in 50 million during approximately 50 years.

Date
Source National Institute of Standards and Technology
Author National Institute of Standards and Technology
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This image is in the public domain in the United States because it is a work of the United States Federal Government, specifically an employee of the National Institute of Standards and Technology, under the terms of Title 17, Chapter 1, Section 105 of the US Code.

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Public domain
This image is in the public domain in the United States because it is a work of the United States Federal Government, specifically an employee of the National Institute of Standards and Technology, under the terms of Title 17, Chapter 1, Section 105 of the US Code.

English | Nederlands | +/−

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