As of May 20, 2019, there is a new kilogram. The old kilogram was based on a platinum-iridium alloy – a shiny metal plug under a bell jar – housed at the Institutes of Standards and Technology. Its name is K4, the fourth copy of LeGrand K, housed at the International Bureau of Weights and Measures in Serres, France. There are seven copies of LeGrand at various sites, against which all weights are calculated, including the pound, at 0.4539237 kilo.
On May 20, 2019, weights around the world changed to the Planck constant. It turns out LeGrand K has been cheating because since its original forging 130 years ago, it has been evaporating. Fifty micrograms (the weight of an eyelash) of this standard weight has been lost to platinum-iridium evaporation.
The Planck constant is not erodible. The Planck constant, a factor of quantum mechanics, is highly precise – if a touch hard to explain at the butcher shop when all you want is a kilo of hot dogs.
My friend Kerry was a weights-and-measures man for the USDA. He traveled the north end of Wisconsin testing and calibrating scales in grocery stores, butcher shops, canning plants, feed mills, grain elevators. He didn’t do jewelry stores, which is too bad because jewelry is where this really matters. A carat being 0.00041 of a pound, or about $12,000 when expressed in quality color. The carat being what is involved in the subjugation of the XY chromosome shelling out cold cash to lease the hand of an XX chromosome.
The purpose of a weights-and-measures guy is to make sure it’s a gallon of gas, a gallon of milk, a pound of butter. To this quest, a weights-and-measures agent carries a set of weights: precise weights, precise gallons. This was my friend’s job, as came with a nice pension, a USDA cop. He accordingly has stories of classic departures. Butcher shops. Gas stations. Feedmills. Feedmills had an inherent problem, the scale being attached to the building, and when the wind blew, it tweaked the building, warped the timbers, affected the scale. Then there was snow load. A fact of life, if still altering the scale, a half pound here, a half pound there. The feedmill scale was a monstrosity of cast iron, a chassis with ball bearings the size of shot puts, all of it iron, rusting, where multiple levers transmit the torque to a balance beam on a hair edge, the scale of brass with a sliding fine, all of it eroding. To the end a sack of corn could end up a touch light.
What Weights and Measures International remedied on May 20, 2019, by employing the Planck constant. No more half-pound shy at the local feedmill. Arnott beware. To add the LeGrand K is rounded off to a mere seven places – 0.4539237 – which leaves a lot of decimal inaccuracy when there are only 1082 atoms in the known universe.
The Planck constant kilogram is 6.626070 x 10-34 kg, as may sound more confusing than 50 microns evaporating from a plutonium alloy.
Accuracy in measure is a historic goal. The meter of the Napoleon era was a pendulum second, the distance traveled by a pendulum in one second. Downside, this meter varied with the pull of gravity. A second standard was set at one ten-millionth of the distance from the North Pole to the equator, which, as it turned out, was variable. In 1887, the LeGrand meter became a single platinum bar. In 1960, the standard was changed to the wavelength of light emitted by Krypton 86. In 1983, the most recent occultation, a meter became the distance light traveled in a vacuum in one 299,792,458th of a second – the speed of light being routine unless one happens to be near a black hole.
Now enter the Kibble balance. The Kibble balance equates the mass of any object to an equivalent electrical current: the E = mc2 business, where mass and energy are but different phases of the other. To the end everything has a Planck constant.
We all know people who lean on the bathroom counter when they weigh themselves in the morning. The Planck constant bathroom scale is designed for such cheaters.