How do we actually build the new kilogram?

Once upon a time the kilogram was a piece of metal preserved in a vault located in a basement. If I needed to build a high precision balance all I needed to do was tuning the the value of my kilograms to that piece of metal.

Things changed in 2019 and the kilogram got redefined. Not anymore exactly equal to a piece of metal preserved in a vault located in a basement, but exactly equal to $$\frac{h}{c^2}$$ multiplied by a ridiculously large number ($$1.356392489652 \times 10^{50}$$ hertz).

But I am still a balance manufacturer. How do I tune my kilograms to this exact new value? And how can anyone do it – even allowing some uncertainty?

• You talk to your local primary standards lab. Now, what they do is your question… Dec 18, 2021 at 15:42
• If you have some LEGO lying around, you can build one like that. Dec 18, 2021 at 20:40