The need for reliable measurement is almost as old as mankind itself. From the earliest times, reliable weight, liquid and length measurements were required for trade and construction, while observing the stars
led to sophisticated timekeeping.
The requirement for increasingly sophisticated measurements has grown, until today we have an evolving global system of units – the SI.
The SI is about to undergo what could be considered its biggest and final change. It is proposed that in 2018, the SI will be redefined in terms of fundamental constants of nature, and will from that time be unchanging.