Solved cryptogram
The Avogadro constant is a counting number rather than a measurement, and its value is exact.
Physics Facts, sourced to NIST.
What it means
For a long time this number was something to be measured, and successive experiments narrowed it down. Since the 2019 revision of the international system it is fixed by definition instead, so the uncertainty on it is zero. That flips the relationship: chemists no longer measure the constant, they use it to define what a mole is, and the experiments that once targeted it now measure other things.
The claim comes from NIST, and the page it comes from was read on 2026-08-27 to confirm it still says this.
This is not the kind of claim that goes out of date, which is why it was set as a puzzle rather than a fact with a shelf life.
Solve it yourself
This fact is a cryptogram here: 76 letters over 18 different ones, graded medium.
- SourceNIST
- CollectionPhysics Facts
- Difficultymedium
- Length76 letters, 18 of them different
Nearby in the collection
The facts either side of this one.
About as hard as this one
Scored closest to it by the model behind our guide to solving cryptograms.