An Instruction for All Time

The kilogram has just been redefined. Is there one constant in life that never changes?

Measurement may not sound like a topic needing a lot of study, but some scientists do exactly that, and those who do are called metrologists — from the Greek metron which means “measure.” Their work is important.

For example, some metrologists work at the National Institute of Standards and Technology (NIST), a federal agency within the U.S. Department of Commerce. Its mission is “to promote U.S. innovation and industrial competitiveness by advancing measurement science, standards and technology in ways that enhance economic security and improve our quality of life.”

So what do metrologists do to mark a landmark step forward in their field of study?

At least some of them get a themed tattoo.

That’s what six researchers at NIST did late last year after a vote in Versailles, France, where representatives from the United States and 59 other nations voted to change the definition of the kilogram and three other units of measurement (the ampere,...