There’s long been debate over the accuracy of the standardised kilogram. Now, scientists have shown once and for all that the lump of metal defining the unit of mass has been putting on some weight.
We’ve long known that there were some issues with France’s ‘Le Grand K’, the international prototype for what a kilogram really is. Made in 1879 from platinum and iridium alloy, it is the perfect standard for what a kilogram weighs. The problem is it’s losing weight.