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posted by n1 on Thursday October 15 2015, @09:19PM   Printer-friendly
from the about-the-same-as-a-bag-of-sugar dept.

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.


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  • (Score: 2) by Magic Oddball on Friday October 16 2015, @02:09AM

    by Magic Oddball (3847) on Friday October 16 2015, @02:09AM (#250369) Journal

    A few more good examples, though mostly horse-related:

    • 1 hand = 4" | 10cm (orig. width of a man's palm across the knuckles)
    • 1 length = 8' | 2.4m (distance from a horse's nose to its tail)
    • 1 furlong = ⅛ mile | 220 yards | 201m (orig. length of a standard furrow)
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  • (Score: 2) by tangomargarine on Friday October 16 2015, @02:37AM

    by tangomargarine (667) on Friday October 16 2015, @02:37AM (#250378)

    What the heck is a "standard furrow"?

    --
    "Is that really true?" "I just spent the last hour telling you to think for yourself! Didn't you hear anything I said?"
    • (Score: 0) by Anonymous Coward on Friday October 16 2015, @06:41AM

      by Anonymous Coward on Friday October 16 2015, @06:41AM (#250436)

      About how far oxen can pull a plow before needing a rest.