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, ...

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, ...

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 ...

In a subterranean vault in a suburb of Paris lies a small, rarely seen metal cylinder known as Le Grand K. For 130 years, this golf-ball-sized hunk of 90% platinum and 10% iridium has served as the ...

Weighty matters: a platinum-iridium kilogram belonging to the US National Institute of standards and Technology. (Courtesy: J.L. Lee/NIST) Metrologists and policy-makers from 60 countries around the ...

All change: work on the redefinition of the kilogram was carried out using a Kibble balance. (Courtesy: BIPM) The redefinition of four units of the International System of Units (SI) will come into ...

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 ...

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, ...

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 ...