International prototypes of the metre and kilogram
Prototipos internacionales del metro y del kilogramo
- Date
- 1889 · confidence high
- Place
- Sèvres, Île-de-France, France
- Credited to
- International Bureau of Weights and Measures
- Field
- Knowledge & symbols
What it is
A platinum-iridium bar (metre) and cylinder of the same metal (kilogram) approved at the first General Conference on Weights and Measures (1889), with numbered copies for the Member States. The kilogram was defined by it until 2019, the last material standard of mass.
The kilogram prototype ('Le Grand K') drifts in mass relative to its copies (about 50 micrograms over a century), which hastened its replacement. The metre was already redefined in 1960.
What it led to
- the definition of the kilogram until 2019
- national copies and periodic mass comparisons
- the motivation for redefining the kilogram with Planck's constant