Tracing back to 1410, the Prague Astronomical Clock in the Czech Republic stands as the oldest operational mechanical tracker of celestial events. Its pioneering display of the relative positions of the sun, moon, and zodiac underlines the brilliance and innovation of early scholars and engineers. Many subsequent watches, including Richard of Wallingford’s 1330 clock and the 1364 Astrarium by Italian engineer Giovanni Dondi, tracked the sun, moon, and known planets with verifiable precision.

Transitioning such complex astronomical complications from colossal clock towers to wearable timepieces, however, was no easy task. The advent of portable time in the early 16th century, thanks to Peter Henlein’s spring-driven Nuremberg eggs, marked the beginning of this transition. Despite the inaccuracy of their rudimentary moon phase indicators, these portable timekeepers were milestones for future advancements.