Sevres.science / Articles
Articles
Short answers to practical questions about units and measurement, each based on primary sources.
What is UTC? How world time is made
World time is computed in Sèvres from hundreds of atomic clocks, and every country’s clocks are compared against it.
Why the kilogram is no longer a metal cylinder
For 130 years the kilogram was one cylinder in a vault in Sèvres. Since 2019 it is fixed by the Planck constant, and nothing on your scales changed.
20 °C or 20°C? How to write degrees Celsius
Put a space between the number and the symbol: 20 °C. The only exception is the degree of angle.
Kilobyte: 1000 or 1024 bytes?
In the SI a kilobyte is exactly 1000 bytes. The 1024-byte unit has its own name: the kibibyte.