Our ancient ancestors first made measurements using their hands and feet or a primate calendar painted on cave walls but once humans started building grand projects for their gods, such as the sun god Ra, things needed to be more exact. The cubit rod made sure the Egyptians’ pyramids met at the top.

Deep underground in a vault beneath Paris, which no army has dared invade, lives the definitive kilogram. But there is a problem; it’s losing weight! This program charts the history of mass measurement and the modern-day race to replace the Kilo with something more stable.

From lightning bolts and Watt engines to electromagnetic waves and single electrons, our final program looks at the measurement of light, electricity, and heat. We’ve been using light to communicate for millennia, with fire beacons saving the British Isles from invasion.