SINGAPORE — A kilogram is hard to fathom. It is a unit of mass, but humans can only sense force and not mass, hence the frequent confusion between mass and weight, which is a type of force, said Mr ...

PARIS — A kilogram just isn't what it used to be. The 118-year-old cylinder that is the international prototype for the metric mass, kept tightly under lock and key outside Paris, is mysteriously ...

But the kilogram prototype, known as “Le Grand K,” was made by humans and is subject to all our limitations. It is inaccessible — the safe containing the cylinder can be opened only by three ...

Humanity is on the verge of a weighty achievement. On Friday, representatives of more than 60 nations will convene in Versailles, France, to approve a new definition for the kilogram. Since the 19th ...