THE KEYS TO ACCURACY
The International Prototype Kilogram
‘K’ is kept hidden in a basement at
the BIPM in Sèvres. Once every year,
the three persons guarding the keys
to the vault join to open it for eyeball
inspection of ‘K’ during a little cere-
mony: the BIPM's director, the head
of the French National Archive, and
the president of the CIPM.
They cover the teeth of the ancient
skeleton keys for fear they might be
reproduced from the photo.