A plum-sized lump of metal takes us from the French Revolution to an underground bunker in Maryland as we try to weigh the way we weigh the world around us.

In this short, 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.