Say Goodbye To The Original Kilogram

Scientists are preparing to dethrone the ‘king of kilograms’ – the defining mass against which all other kilograms are measured.

Le Grand K, stored under secure lock and key in France since it was made in 1889, is getting an upgrade to a modernised device that measures light.

Scientists hope to retire the carefully calibrated alloy cylinder to provide security to the world’s metric weight systems should the object be destroyed.

Kept under two bell jars and secured by three keys – only two of which are in France – the precious hunk of metal is stored in an elegant building just outside Paris.

It has served as the global standard for weighing things for 130 years, with dozens of copies stored across the globe to standardise the weights of individual nations.

 Le Grand K (right) is an alloy cylinder used to standardise the kilo for more than a century and has been kept under secure lock and key in Paris since it was made in 1889. The weight is stored under two bell jars (centre) to stop it from accruing dust and dirt

Britain’s own version is stored in the National Physical Laboratory (NPL) in London, where scientists have spent decades developing a new global weight standard.

The device, known as a Kibble balance, tracks tiny changes in electrical current to calculate the gravitational force acting on a mass – the two components of weight.

It could spell the end for Le Grand K, which has been stored in the Louis XIV Pavillon de Breteuil, a building in the small French town of Saint-Cloud, for 130 years.

‘One key reason for doing this work is to provide international security,’ Ian Robinson, head of engineering measurement at the NPL, told the Luxembourg-based magazine Delano.

‘If the Pavillon de Breteuil burned down tomorrow and the kilogram in its vaults melted, we would have no reference left for the world’s metric weights system.