N·01
Pi — the circle constant
3.14159 …
In the record
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An archive of the constants
A fixed point in a changing field.
Some numbers do not move. The world is built to their shape, and they hold — across every instrument, every language, every century. This is a small archive of them.
Enter the index
The index
Nine numbers, chosen for how little they change.
A constant is a value that stays the same wherever and whenever it is measured. Some are set exactly by agreement; others have been chased for centuries and still yield only a handful of digits. Open any card to read its record.
A constant is a promise the universe keeps without being asked.
There are two kinds here. Some are fixed by decree. In 2019 the world's metrologists redrew the units of measurement around a handful of numbers — the speed of light, the Planck constant, Avogadro's number — and declared them exact. They no longer have uncertainty because we no longer measure them; we measure everything else against them.
The rest are earned. Gravity's constant has resisted two hundred years of ever-finer instruments and still gives up only five reliable digits. The fine-structure constant is known to ten, and no one can say why it is what it is. These are the numbers we chase rather than choose — and their stubbornness is its own kind of permanence.
NRADAR keeps both, plainly and without embellishment. Nothing on this page is scheduled to change.
A number we missed?
If there's a constant that belongs in the record, or a correction to one that's here, the archive is listening.