From the sky to the wrist: how perpetual calendars work

Since the earliest times, humans have looked to the skies to measure time. The movements of the sun, moon and stars helped them determine the precise day, date and time, something that still inspires wonder – from children gazing up at the night sky to astronomers charting distant galaxies. Perpetual calendars, including those crafted by Audemars Piguet, translate the principles of astronomy and the Gregorian calendar into high watchmaking – an intricate blend of art, mechanics and design. At...