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. googletag.cmd.push(function() { googletag.display(‘div-gpt-ad-1449240174198-2′); }); 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. You won’t notice anything—you will not be heavier or lighter than yesterday—because the transition has been made to be seamless. Just the definitions of the seven base units of the SI (Système International d’Unités, or the International System of Units) are now completely different from yesterday. Humans have always been able to count, but as we evolved we quickly moved to measuring lengths, weights and time. The Egyptian Pharaohs caused pyramids to be built based on the length of the royal forearm, known as the Royal Cubit. This was kept and promulgated by engineer priests who maintained the standard under pain ...