This is the "International Prototype Kilogram", and the hilarious house it lives in. It's a palladium-iridium alloy, and it sits in a vault in Sévres, France all day, every day. Its mass currently defines the kilogram. BUT NOT FOR LONG.
Apparently, the kilogram needs a dusting off and an oil check. Using the palladium-iridium French rod isn't ideal, because all things physical deteriorate, albeit some more slowly than others. So, at
a conference in London, two separate groups are trying to define the kilogram in terms of unchanging natural constants, specifically Planck's constant and Avogadro's number. However, the two methods don't give a definition for the kilogram that agrees. The proposed solution? Just average them. As you might expect, a lot of physicists have their undies all up in a knot about it —
The compromise seems to run contrary to the exacting standards of metrology, but without it, the kilogram's redefinition could be delayed for years or even decades. "In some sense, the redefinition of the kilogram is being held hostage," [Richard] Davis [former head of the mass division at the International Bureau of Weights and Measures (BIPM)] told conference attendees.
So much drama at the Royal Society, it's kinda hard being an S - I - U - N - I -T.
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