Chapter 12 of The Knowledge explains how you can go right back to first principles to work out how to tell the time for yourself. Planting a stick into the ground can serve as a simple sundial, with the hour of the day indicated as the shadow revolves around with the movement of the sun. This chronological technology has been used by humanity for thousands of years.
But now, sundials have been brought right up into the 21st century.
Julien Coyne has invented a sundial that indicates the time as a digital display. This astounding example of ingenuity is based on some very clever mathematical design and 3D printing of the gnomon. Once orientated correctly, the sunlight passes through the precisely-calculated slits in the gnomon to project a shadow that indicates the time as a digital display.
Watch the digital sundial in action below, and buy your own on Etsy!