30 Apr '12, 5pm

The Kilogram, Reinvented

Photo: Robert Rathe/National Institute of Standards and Technology Once a year, three officials bearing three separate keys meet at the bottom of a stairwell at the International Bureau of Weights and Measures, in Sèvres, France. There they unlock a vault to check that a plum-size cylinder of platinum iridium alloy is exactly where it should be. Then they close the vault and leave the cylinder to sit alone, under three concentric bell jars, as it has for most of the past 125 years.
 This lonely cylinder is the International Prototype of the Kilogram , known colloquially as Le Grand K, and it is the last remaining physical object to define a unit of measure. It’s a quaint throwback to a time when people compared the ocean’s depth to the span of a man’s outstretched arms and the second to a tiny fraction of a year. Now we fix our rulers to the speed of light and our clocks t...

Full article: http://spectrum.ieee.org/consumer-electronics/standards/t...

Tweets

Did u know that the kilogram value we use is determined by a platinum iridium alloy cylinder, Le Grand K?

Did u know that the kilogram value we use is de...

spectrum.ieee.org 13 May '12, 5am

Photo: Robert Rathe/National Institute of Standards and Technology Once a year, three officials bearing three separate key...