
Disseminating the New Kilogram: An International ‘Dry Run’ - amexrap
https://www.nist.gov/news-events/news/2016/11/disseminating-new-kilogram-international-dry-run
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semi-extrinsic
Fun fact: while mainly dealing with insane precision machines, NIST have also
designed a LEGO watt balance that you can use to determine mass based on the
new SI standard in the comfort of your own home:

[http://scitation.aip.org/content/aapt/journal/ajp/83/11/10.1...](http://scitation.aip.org/content/aapt/journal/ajp/83/11/10.1119/1.4929898)

(Open Access)

~~~
Animats
That's very neat. It relies on the accuracy of the electrical current
measurements, though; it's not an absolute measurement from fundamental
physics.

For that, NIST has a fundamental standard for the standard volt.[1] So the
fundamental standards now are time (atomic clock), the speed of light in
vacuum, and the standard volt. The meter is now defined in terms of the speed
of light in vacuum and a time.

[1] [https://www.nist.gov/news-events/news/2013/04/primary-
voltag...](https://www.nist.gov/news-events/news/2013/04/primary-voltage-
standard-whole-world)

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jgable
Has anyone here worked in a laboratory or other environment that uses these
reference masses and requires this level of precision?

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mdturnerphys
Not directly, but my research group has used referenced masses and a former
colleague works on the NIST watt balance.

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source99
It's worth watching the video just for the sound effects.

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dexwiz
Wow the was... bad. I can get scientists want to bring SciFi to life, but this
is a stretch.

In the second Artemis Fowl book, there is a centaur who uses a human laptop
(magical creatures live in a technologically advanced society underground),
and the first thing he does is mute it. He complains that humans are unevolved
and have some sort of compulsion to make their products emit sounds and and
lights.

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haneefmubarak
Foaly was the best!

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jelder
Why does the video have goofy sound effects?

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mimsee
It says under the video "All sound effects added; the actual process is
extremely quiet."

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acqq
More about the whole process:

[http://www.nature.com/news/kilogram-conflict-resolved-at-
las...](http://www.nature.com/news/kilogram-conflict-resolved-at-last-1.18550)

Kilogram conflict resolved at last (2015)

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dsjoerg
it's embarrassing that we use such a fragile process to establish a standard
that is supposed to be used everywhere.

~~~
jasonmp85
I'm not actually sure what you're insinuating here. Previously the standard
WAS the "international prototype kilogram", all of which have drifted since
creation (see here:
[https://en.wikipedia.org/wiki/Kilogram#Stability_of_the_inte...](https://en.wikipedia.org/wiki/Kilogram#Stability_of_the_international_prototype_kilogram)
)

The problem with this is it isn't even fragile, it's _not reproducible_. The
worst part is that other SI units depend on the kilogram, so they all change
as this drift occurs! After a certain amount of time, how will we know what a
"real" kilogram is? See here for discussion of this SI problem:
[https://en.wikipedia.org/wiki/Kilogram#Dependency_of_the_SI_...](https://en.wikipedia.org/wiki/Kilogram#Dependency_of_the_SI_on_the_IPK)

The point of the watt balance approach is to make it possible for a lab to
reproduce the kilogram without another kilogram reference. That's what this is
about, and I don't really think it's embarrassing. I think it's very, very
hard.

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moon_of_moon
Why do we need these rare metals? Why not just use a block of ice generated
from a known quantity of water, for example?

~~~
wolfgang42
I'm not sure why ice would matter given that it should weigh the same as in
the liquid form, but...

How do you measure a known quantity of water to within a few tens of parts per
billion? Do you specify the proportion of light to heavy water? (For 'normal'
water about 1 in 41 million.) What about contaminants in the water? There are
so many uncertainties that it's impossible for all practical purposes.

The whole point of using 'rare' silicon is that we already have commercial
processes for producing ultrapure, defectless, monocrystals of the stuff (for
use in computer chips), so it's easy to reuse that technology for defining a
kilogram.

