Measuring Mass: The Last Artefact

BBC4, 9pm

It affects nearly every aspect of our lives, including the food we eat, the cars we drive and the medicines we take. It is the kilogram, the base unit of mass in the International System of Units, which is represented by a small hunk of metal held in a high-tech vault just outside Paris. Over time, its mass has eroded by the weight of an eyelash and this fascinating film, narrated by Miriam Margolyes, follows the high-stakes, two-year race to redefine it. ★★★★★