We measure stuff all the time – how long, how heavy, how hot, and so on – because we need to for things such as trade, health and knowledge. But making sure our measurements compare apples with apples has been a challenge: how to know if my kilogram weight or metre length is the same as yours.
Attempts have been made to define the units of measurement over the years. But today – International Metrology Day – sees the complete revision of those standards come into play.
Today marks one of the biggest shake-ups in the history of measurement. But the new standards on how we define units of mass, length, time and so on are not easy to explain.