In today’s story, which originally aired in 2014, we meet a very special cylinder. It's the gold standard (or, in this case, the platinum-iridium standard) for measuring mass. For decades it's been coddled and cared for and treated like a tiny king. But, as we learn from writer Andrew Marantz, things change—even things that were specifically designed to stay the same.

Special thanks to Ken Alder, Ari Adland, Eric Perlmutter, Terry Quinn and Richard Davis.

And to the musical group, His Majestys Sagbutts & Cornetts, for the use of their song “Horses and Hounds.”

We have some exciting news! In the “Zoozve” episode, Radiolab named its first-ever quasi-moon, and now it's your turn! Radiolab has teamed up with The International Astronomical Union to launch a global naming contest for one of Earth’s quasi-moons. This is your chance to make your mark on the heavens. Vote on your favorites soon, check here for details: https://radiolab.org/moon

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Leadership support for Radiolab’s science programming is provided by the Gordon and Betty Moore Foundation, Science Sandbox, a Simons Foundation Initiative, and the John Templeton Foundation. Foundational support for Radiolab was provided by the Alfred P. Sloan Foundation.