Solved cryptogram

A second is no longer a slice of the day. It is a fixed count of vibrations in a cesium atom.

Physics Facts, sourced to NIST.

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What it means

Tying time to the Earth turned out to be a bad idea, because the planet's spin is uneven and slowly slowing. A cesium atom is not. Electrons in cesium flip between two energy states at a rate that is the same everywhere in the universe, and the second is defined as a specific number of those flips. Clocks built this way drift by less than a second over the age of the solar system.

The claim comes from NIST.

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