A weighty issue: scientists redefine the kilogram after 129 years

The kilogram will no longer be measured against an actual weight, after scientists voted to start using an electromagnetic current. Since 1889, a kilogram has been defined by a single lump of platinum-iridium which is housed inside three glass bell jars at the headquarters of the International Bureau of Weights and Measures (BIPM) , just outside Paris. But the master copy, known as ‘Le Grand K’, has been picking up microparticles of dust, or losing mass in cleaning, causing consterna