The kilogram just got a revamp. A unit of time might be next

The unit of mass is now defined by a fundamental constant of nature, not a hunk of metal

metal kilogram

HAS-BEEN  For 130 years, this metal cylinder was the definition of a kilogram. Now, it's just another hunk of metal, as scientists have instituted a new definition based on a quantity known as the Planck constant.

BIPM

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