And we actually do: „Though the IPK, the current primary artefact, and its replicas are stored in carefully controlled laboratory conditions, their masses have

And we actually do: „Though the IPK, the current primary artefact, and its replicas are stored in carefully controlled laboratory conditions, their masses have been subject to fluctuation as a result of poorly understood factors, possibly including handling, cleaning and contamination. The IPK has diverged from its replicas by 50 μg since their manufacture late in the 19th century.“ https://en.m.wikipedia.org/wiki/Kilogram https://en.m.wikipedia.org/wiki/Kilogram