Sèvres kilogram and NIST mass-redefinition program

She had said their big problem is they're trying to come up with a uniform standard for mass. The problem is — I told you yesterday — there's still this platinum-iridium mass held in the vault in Sèvres, France, only taken out of the vault about every 10 years. As far as they can tell, it's losing weight at 60 micrograms per century. I went up to her at the break and said, why is this thing losing weight, and how do you know if it's the reference standard? She said, we weighed it against a bunch of other reference standards, and they're either all gaining weight at the same rate, or this one's losing weight. I said, how can it be losing weight? Oh well, platinum oxidizes. Excuse me, I'm a materials scientist, I didn't know platinum oxidized a whole lot. But apparently before they weigh it — it's been in a vault under vacuum — they wipe it down. So they're wearing it away every 10 years when they wipe it with some cloth before they weigh it. It's all statistics. They think it's losing weight, so they want to define it in terms of some non-variable standard.