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Mike Richman


World Metrology Day and the Enduring Importance of the Metre Convention

Published: Wednesday, May 16, 2018 - 11:00

One of the foundations of our modern, technology-based society comes from established and commonly agreed-upon measurements. On May 20 each year, we acknowledge this fact by celebrating World Metrology Day, which is the perfect opportunity to consider the central importance of the science of measurement.

Not everyone knows about World Metrology Day, and fewer still recall the reason why it occurs specifically on May 20. The logic, however, is inescapable—143 years ago, on May 20, 1875, delegates from 30 nations met in Paris to set standard measurements for the meter and the kilogram, and to establish protocols to maintain these and other standards for all scientists, academic institutions, and businesses across the world. The Metre Convention gave birth to the General Conference on Weights and Measures (CGPM), the governing body of metrology to this day.

For those working in large-volume, close-tolerance measurement and alignment, a world without standardized metrology is almost inconceivable. Although many leading industrialized nations prior to 1875 had established standards within their realms, the international flavor of the convention, and the spirit of cooperation it instilled, helped paved the way for the interconnected supply chains and trading partnerships that are the hallmarks of 21st century commerce. Without agreement on weights and measures, the entire system would fall apart.

The building blocks of metrology are the International System of Units (SI), which defines the modern metric system. From a few years shortly after the Metre Convention until quite recently, the base SI were actual things—in other words, a kilogram was a piece of metal, a meter was a length of rod. Those physical samples were the standards that defined weights and measures.

Physical structures, however, degrade, even if ever so slightly and ever so slowly. And because the science of measurement demands nothing less than absolute precision, it became apparent that the SI needed updating for a new and more accurate age.

For this reason, the CGPM is now in the process of converting the seven SI base units to unchangeable natural constants. For example, no longer is the meter defined by the length of a bar—now it’s the length of a path that light travels (in a vacuum) during 1/299,792,458 of a second. See what I mean by precision?

All seven SI base units will eventually be pegged to universal constants like the Boltzmann constant (relating temperature to energy) and the Planck constant (relating mass to electromagnetic energy). The CGPM plans to have the SI converted and ready for use by metrologists across the globe by next World Metrology Day—May 20, 2019.

So give a thought this weekend to the meaning of World Metrology Day and the reason why scientists of several generations past gathered in Paris to establish the measurement principles and protocols that echo down to our modern society. The irreplaceable accuracy of industry today, not to mention tomorrow, traces itself back to that precise moment in time.


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Mike Richman