If you ever are in Paris, I can't recommend the Musee des Arts et Metiers enough.
I believe they have the several reference platinum kilograms that are now out of spec. [1]
they also have the original actual Foucault pendulum that was used to demonstrate Earth's rotation. (and a replica doing a live demo, of course)
They have so many incredible artifacts (for weights and measures but also so much more: engineering, physics, civil engineering, machining,...)
They have so many incredible artifacts (for weights and measures but also so much more: engineering, physics, civil engineering, machining,...)
[1]: https://collections.arts-et-metiers.net?id=13404-0001-