If scientists had sacred objects, this would be one of them: a single, closely guarded 137-year-old cylinder of metal, housed in a vault outside of Paris. It is a prototype that precisely defines a ...

The kilogram finally has a precise meaning despite defying a rigorous definition for over a century. Delegates of the General Conference on Weights and Measures unanimously voted Nov. 16 in favor of a ...

If several scientists get their way, a 2.2-pound hunk of metal -- the international prototype of the kilogram -- may soon be out of style. Like its six basic-units-of-measurement siblings before it -- ...