Kopien Nr. 4 und Nr. 20 des Internationalen Kilogrammprototyps von 1890 für die USA. Das Urkilogramm wird in Sèvres bei Paris aufbewahrt. Beschreibung: «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.» // Fotograf: unbekannt // Standort: National Institute of Standards and Technology, USA

Digitalisat: National Institute of Standards and Technology // Quelle: Wikimedia Commons // Lizenz: Public Domain