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Re: The Kilogram: The Scientific Unit with a Serious Weight Problem!

Active Participant RER
Active Participant

Within the next few years, an ingenious device called the ‘Watt Balance’ will fundamentally redefine the kilogram! An Austin-based YouTuber has used the NI platform to explain this complex instrument, in a supremely accessibly way.

In the late 1800s, a plum-sized metal cylinder was forged in London, using a combination of platinum and iridium. This unassuming hunk of metal was promptly shipped to a France, where Parisian scientists polished and weighed it… then polished and weighed it… then polished and weighed it again… until they finally determined that it was exactly one kilogram.
Le Grand K 2.png

 That’s how this humble, little cylinder became the International Prototype Kilogram, more affectionately known as Le Grand K. For over 125 years, it’s been the standard against which every other kilogram on the planet is judged! Vive Le Grand K!


Weight for it!

Despite being sealed under three evacuated glass bell-jars… in a climate controlled room… in a heavily-guarded, subterranean vault… Le Grand K seems to have developed a weight loss problem!


Once every 40 years, Le Grand K is removed from its hermetically sealed home, to be compared against similar replicas from around the world. At its most recent weigh-in, it was found to be 0.05 milligrams (approx. the weight of a grain of sand) lighter than its copies.

Did Le Grand K lose mass? Or have the replicas gained mass? No one knows. But it certainly brings doubt into mass measurement! In turn, this brings nagging uncertainty to the dozens of scientific units that are derived from the kilogram (includes Amp, Watt, Newton, Joule, Candela … etc). 


Watt's The Solution

For several decades, metrologists have strived to redefine the kilogram, as a means of retiring ‘Le Grand K’ (edit: I hope I get an invite to the old guy’s retirement bash, its sure to be one hell of a party). Rather than a physical artefact, the redefined kilogram would be based on quantum properties and the unwavering constants of nature.


Scientists at the National Institute of Standards and Technology (NIST) are quickly closing-in on the rebooted kilogram, thanks to an ingenious instrument known as the Watt Balance.


Can I explain how the Watt Balance works? Hell no! Do I know a guy who can? Hell yeah! Grady Hillhouse, a civil engineer based in Austin, Texas, who runs an informative yet gloriously accessible YouTube channel called Practical Engineering. 

DIY Watt Balance


Having used the NI platform to empower his own DIY Watt Balance, the latest Practical Engineering video uses live demonstrations to explain this game-changing instrument. A must see video for curious engineers and scientists everywhere!



Redefining the Kilogram with the DIY Watt Balance


Rich R

Staff Marketing Engineer
National Instruments UK & Ireland
Trusted Enthusiast


for scientific correctness one might add that the Watt balance is one of two favored methods aiming to redefine the kilogram, the other favored approach is to count the number of atoms in a sample of isotopically pure material