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For decades, metrologists have strived to retire ‘Le Grand K’ — the platinum and iridium cylinder that for 126 years has defined the kilogram from a high-security vault outside Paris. Now it looks as if they at last have the data needed to replace the cylinder with a definition based on mathematical constants.
The breakthrough comes in time for the kilogram to be included in a broader redefinition of units — including the ampere, mole and kelvin — scheduled for 2018. And this week, the International Committee for Weights and Measures (CIPM) will meet in Paris to thrash out the next steps.
“It is an exciting time,” says David Newell, a physicist at the US National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland. “It is the culmination of intense, prolonged efforts worldwide.”
[...] In 2011, the CIPM formally agreed to express the kilogram in terms of Planck’s constant, which relates a particle’s energy to its frequency, and, through E = mc2, to its mass. This means first setting the Planck value using experiments based on the current reference kilogram, and then using that value to define the kilogram. The CIPM’s committee on mass recommends that three independent measurements of Planck’s constant agree, and that two of them use different methods.
(Score: 2) by RedBear on Friday October 16 2015, @04:49AM
My question would immediately be how this will effect the current pound/kilogram conversion factor. I was fascinated to learn several years ago that there is a precise decimal conversion factor that was agreed upon by international committee at some point, which is that 1 Pound equals exactly 0.45359237 Kilogram. I had designed a FileMaker* database to run the production data for a seafood plant that processed nearly a million pounds of product per day, and I wanted to most accurate LB-KG conversion possible, so I built that precise conversion factor into every relevant conversion calculation and then rounded appropriately to the task at hand. Other people making invoices and tracking production by hand ended up with slightly different numbers since they thought it was fine to use something as inaccurate as 2.204 (or 2.2046 at best), which was not precise enough to keep the very large numbers accurate as they accumulated into the tens of millions of pounds.
Anyway, I'm wondering if the definition of the kilogram will change sufficiently that they will need to change this official exact conversion factor, or whether the slightly modified mass of the kilogram definition will actually change the very definition of the precise mass of a "pound", while keeping the same conversion factor. I'm assuming the latter. I can't be sure but I think I recall reading somewhere that pretty much all measurement units are officially defined these days based on their relationship to the kilogram or the meter. If they changed the conversion factor it would screw up an extraordinary amount of software around the world.
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* Don't laugh, it worked exceptionally well, much better than I expected actually, and certainly much better than the poorly designed Microsoft SQL monstrosity they've replaced it with since I left.
¯\_ʕ◔.◔ʔ_/¯ LOL. I dunno. I'm just a bear.
... Peace out. Got bear stuff to do. 彡ʕ⌐■.■ʔ
(Score: 1, Informative) by Anonymous Coward on Friday October 16 2015, @03:00PM
Not at all. It won't even affect it.
They are not planning to give the kilogram a new value, they are planning to define a new way to determine it. It will be defined so that, to the measurement accuracy available, the new value will be the same as the old value.