Though we usually assume that distances are fixed (a mile is a mile is a mile) the official definition of a meter has changed numerous times through out history.
Each time, the definition of a meter became more precise, but it also changed slightly from the previous definition, allowing for less and less of the variation inherent in each measuring system.
Bonus: The only three countries not currently using the metric system: Liberia, Myanmar, and the United States.
[Good Magazine – Weights And Measures]
[Via: swissmiss]
