Solved cryptogram
The kilogram was a metal cylinder locked in a vault in France until physics replaced it.
Physics Facts, sourced to NIST.
What it means
The cylinder was cast in 1889 from platinum and iridium, and for well over a century it simply was the kilogram by definition. That was awkward, because it appeared to be losing mass relative to its own official copies, and nobody could say which of them had changed. Since 2019 the kilogram is derived from the Planck constant instead, so the unit no longer depends on an object that can be dropped, scratched or stolen.
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This is not the kind of claim that goes out of date, which is why it was set as a puzzle rather than a fact with a shelf life.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: 72 letters over 21 different ones, graded medium.
- SourceNIST
- CollectionPhysics Facts
- Difficultymedium
- Length72 letters, 21 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.
- Royal Society of Chemistrymedium, 68 letters
- NISThard, 74 letters
- NISTmedium, 72 letters
- NISTmedium, 72 letters