October 18, 2010 marked the 50th anniversary of the International System of Units, also known as the SI System. Resolution 12 of the 11th meeting of the CGPM (1960) established the system as the world ...

These units, together with the astronomical second (based on the mean solar day) as the unit of time, constituted a mechanical unit system. Following the introduction of the ampere, the kelvin and the ...

In addition to other scientific units, the kilogram also is now defined by a natural constant. This is made possible by single crystals grown from highly enriched silicon-28. In addition to Ampere, ...

A flaw in the system leaves physicists grappling with dimensionless units. Water is a precious resource. So protest erupted when, last September, India’s Supreme Court ordered Karnataka state to ...

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 ...

Meet the metric system’s newest prefixes: ronna-, quetta-, ronto- and quecto-. Science News spoke with Richard Brown, head of metrology at the National Physical Laboratory in Teddington, England, ...

It doesn’t happen too often, but after a vote that took place earlier today near Paris, science textbooks really will have to be rewritten. At the Congress Chamber in the Palace of Versailles, ...

The United States's version of the Imperial system is based on an older British version. MaxPixel At press time, only three of the world's countries don't use the metric system: the United States, ...

The kilogram — anywhere in the world, for any purpose — is based on the exact weight of a golf-ball-sized chunk of platinum and iridium stored under three glass bell jars in a vault in an ornate ...

In addition to Ampere, Kelvin, Mol and Co., the kilogram also is now defined by a natural constant. In concrete terms, this means that the original kilogram, which has been the measure of all things ...