France – and the majority of the rest of the world – is marking 150 years since the Metre Convention first united them in a shared language of measurement, laying the foundations for international scientific cooperation.
There aren't many 136-year-old metal cylinders tucked away in Paris basements that can claim global fame.
Yet "Prototype 35" – a shimmering iridium-platinum artefact – quietly changed the course of modern life.
At just 39 millimetres high and wide, this unassuming 1 kilogram weight helped anchor the world’s understanding of mass – and with it, the uniformity of measurement that underpins everything from baking a cake to building a bridge.
This week marked the 150th anniversary of the Metre Convention, signed in Paris on 20 May, 1875 by 17 nations eager to bring order to a chaotic patchwork of global measurements.
The treaty established a universal system of units – ushering in consistency, accuracy, and international cooperation in science, industry and daily life.
As the French national metrology institute posted in celebration on X: "This international convention laid the foundations for scientific cooperation to harmonise measurements across the world".
Revolutionary beginnings
Before the Convention, the world was a confusing place.
A pound of wheat in Marseille didn’t weigh the same as one in Brest, and a yard in one city might be a foot in another.
The French Revolution, with its rallying cry for equality, prompted scientists to invent the metric system, based not on arbitrary traditions but on nature itself, with the metre originally defined as a fraction of Earth’s meridian.
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What began as a revolutionary idea soon gained traction beyond France. The 1875 Convention established the International Bureau of Weights and Measures and marked the beginning of a truly global system.
Today, more than 150 countries use the International System of Units, which comprises seven base measurements: the metre, kilogram, second, kelvin, candela, ampere and mole.
Far from being stuck in the past, this system is constantly evolving.
Gone are the days of relying on physical objects such as Prototype 35 as ultimate standards. Instead, modern definitions rest on fundamental constants of nature. The metre, for example, is now linked to the speed of light and the kilogram to Planck’s constant, a cornerstone of quantum physics.
International cooperation
These definitions require practical application, and that’s where national metrology institutes such as France’s LNE come in.
At its laboratory in Paris, scientists including Florian Beaudoux meticulously calibrate masses, lasers and gauge blocks, ensuring precision across industries. "Even a microscopic miscalculation can affect everything from engineering to medicine," he explained to French news agency AFP.
Their work ensures that a litre of petrol in Lyon matches one in Lagos, that an aircraft part built in Toulouse fits seamlessly with another from Hamburg, and that a blood test result is identical whether processed in Tokyo or Toronto.
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International cooperation is at the heart of what they do. As Maguelonne Chambon, director of research at LNE, said: "We need to compare ourselves, understand differences and agree on how to resolve them."
With climate, altitude and even gravity varying across the globe, collaboration is not a luxury but a necessity.
(with newswires)
