How the metre changed the world

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Nowdays, if you want to find out how long one metre is, you can use a tape measure or, if you are a scientist, you can calculate the distance that light travels in a vacuum in 1/299 792 458 seconds. But how did we decide on what length a metre should be in the first place? To follow the far-from-straight story of the metre Quentin Cooper is joined by Professor Robert Crease, historian of science at Stonybrook University in the USA; Professor Marc Himbert, Scientific director of the Metrology Laboratory at CNAM in Paris; and Dr. Jahnavi Phalkey, historian of contemporary and twentieth century science and technology at King’s College in London. Photo: Lilian Bourgeat's art creation 'Tape Measure', France 2013 (Getty Images)