THE MOLE—as in 6.02214076×10^23, the unit in chemistry used to count really really tiny stuff like atoms and molecules. Well, THE MOLE changed (it’s not simply 6.022×10^23 anymore). And while you may not have noticed it, a fundamental shift in the way we measure things—not just on Earth, but throughout space and time—took place when the new mole was born.

The mole is one of the units of measurement in the seven base units in the International System of Units, which includes second, metre, kilogram, ampere, kelvin, and candela. Four of those, including the mole, were officially redefined forever on May 20, 2019 thanks to the work of National Institute of Standards and Technology (NIST) chemists Bob Vocke and Savelas Rabb, and an international team of scientists.

This PopSci Experimentals explainer by Tom McNamara, with narration by Eleanor Cummins and animation design by Ben Gabelman and Jason Drakeford, teams up with Vocke and Rabb to better understand this more perfect unit: The New Mole.

The three-part video not only defines moles, counts atoms, and gets a look at one of the most perfectly round things in the world, but it also explores science history and helps explain why such a precise calculation of something we can’t see is so important.

More about why it matters from NIST:

For about 20 years, the international community worked on the modern redefinition of the mole. This effort centered on an amazingly ultra-pure sphere of one of the world’s most common elements: silicon. But unlike the kilogram ingot in France, this one doesn’t sit in a little vault somewhere to be used for reference. Instead, the equations themselves are the reference. The sphere serves as evidence that the equation works.

And scientists have finally achieved what French revolutionaries envisioned when they created the SI: a measurement system for all times and for all people.

Even describing the scientific work that Vocke and Rabb finished involving the sphere brings a contrarian smile to Vocke’s face. No one has to be beholden to a drifting artifact anymore. It is as if a king has been dethroned or a monarchy toppled, and it seems as if that appeals to the rebellious side of Vocke’s personality.

What Vocke wants, really, is for the public to grasp the importance of what has just happened. This isn’t about reputation or professional pride. This is about leveling the playing field. An important part of his vocation has been democratized, thanks to international cooperation between scientific teams from all over the globe. Now, no one needs to travel to France and get permission to compare their measurement of mass to a special kilogram artifact in a little vault.

Related reading: The Avogadro constant, the International Avogadro Project, the Kibble Balance, mass spectrometry, and silicon.

Then explore more videos about measurements, more elements, and more science history videos on TKSST, including Animated Life: Seeing the Invisible, Why America Still Uses Fahrenheit, and why the metric system matters.