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...