The official definition of a kilogram has been changing for well over a century, but this week it may be redefined for the final time. After years of debate and discussion, scientists from around the ...

The Latest on a scientific meeting on how to define weights and measures (all times local): 1:35 p.m. The international system of measurements has been overhauled with new definitions for the kilogram ...

Deep underneath the Parisian suburb of Saint-Cloud, in a vault that can only be opened by three people wielding three different keys, there lies a hunk of metal that is so crucial to the world of ...