The State of the Unit: a documentary film about the redefinition of the kilogram

March 18, 2016 Stop-Motion Animation and the Kilogram Migration

Homemade miniature replicas of the temoins and IPK.

I am working on some stop-motion animation footage, to show what I call the "Migration of the Kilograms" — when in 1889 kilograms were assigned to the 17 countries who signed the Metre Convention of 1875. I made some replicas of that batch of kilograms.

Here you see a miniature of Kilogram 8/41. They made 40 kilograms and engraved each with a number. When they got to the end, they had one leftover and no number '8'. So it was engraved with '41'. The replica shown is made of clay and not engraved with anything other than my fingerprints.

Richard Davis told me this story of K8/41 and I like the contrast of über-precise kilograms and a simple mistake in counting to 40. He gives details about the kilograms histories and the Metre Convention in his paper "The SI unit of mass," Metrologia 40 (2003) p. 299–305. His paper also includes two photographs of the témoins, which is French for witness, second, or best man. The témoins live in the same vault with the IPK, in an undisclosed location at the BIPM.

Unlike my clay miniatures, they are "real copies" of the IPK—which seems to me an oxymoron.