Rollout May 20, 2019 of revised SI measurement standards; no longer dependent on physical objects but on physical constants

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 standard