The Standard Unit — Somebody had to decide what a metre is
Front
The Standard Unit
Somebody had to decide what a metre is
The agreed definitions that let separately made parts fit together.
Back
Interchangeable parts require that a millimetre mean the same thing in two factories on two continents. For most of history it did not. Standards bodies pinned each unit to something anyone could reproduce: the metre now comes from the speed of light, and the kilogram from a constant of physics.
- The kilogram was redefined in 2019. Until then the world's master unit of mass was a single platinum-iridium cylinder near Paris, and it was slowly changing weight.
- Precision costs money. Every extra decimal place of tolerance makes a part harder to make, so good engineers specify the loosest tolerance that still works.
Winchester, The Perfectionists (2018)
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