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>it is roughly five parts in 100 million heavier than all the working standards, which have been leaving behind a few atoms of metal every time they are put on scales

Are the working copies really only shedding such a small number of atoms per use? Just seems like it should be a higher number.

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Well some back of the napkin math, atomic mass of platinum, the heavier constituent of the standard is 195. So more than 5 mols of these atoms are in the block, because 1 mol of pt is 195 grams. So there’s around 5610^23 atoms. So 5 parts per 100 million adds up to a lot. Maybe 1.5*10^15 atoms? It’s been a while since I had chemistry...

Platinum has molar mass ~195g, Iridium ~192g. This means the working copies have between ~5.128 and ~5.208 mol atoms in a kg. Let's round it to 5.2 mol, that's ~3.13 * 10^24 atoms.

Five parts in 100 million is ~1.565 * 10^18 atoms. Sound like a pretty large number to me.

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