As of today, new standard defines the kilogram. (Credit: Shutterstock/Piotr Wytrazek)

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 meter length is the same as yours.

Attempts have been made to define the units of measurement over the years. But today – International Metrology