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Arago Kilogram
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Arago Kilogram

 ca. 1821  On virtual loan from the NIST Automated Production Technology Division
In 1866, Congress legalized (but did not require) use of the metric system in the United States. The Office of Weights and Measures (OWM) was directed to provide each state with one set of standard metric weights and measures. OWM resorted to the Committee Meter, an end-standard that Hassler had brought with him to the United States in 1805, to construct the length standards (an end standard is a metal measuring rod where the standard is the distance between its two end surfaces). To produce metric mass standards, OWM relied on the platinum Arago Kilogram. The Kilogram was made in France by Fortin and certified by the physicist Arago to differ from the original kilogram of the Archives by less than 1 mg. It was procured for the United States in 1821 by Minister to France, Albert Gallatin.

 ca. 1852  NIST Museum Collection

Silbermann Kilogram, historical secondary mass standard