In-Depth: A Guide to Every Equation of Time Watch by A.-L. Breguet
Abraham-Louis Breguet (1747-1823) stands among the most revered names in horology, celebrated for innovations that shaped modern watchmaking. While his tourbillon, self-winding mechanism, and anti-shock system are widely acknowledged, his work in astronomical timekeeping, particularly equation of time (EOT) watches, remain one of Breguet’s most intricate yet less-explored achievements. With 2025 marking the 250th anniversary of his birth, this guide offers the most comprehensive study of every known EOT timepiece made during his lifetime, including pocket watch no. 160 “Marie Antoinette”, expanding on our prior analysis of the complication (in parts I and II). No. 160 as pictured at the recent exhibition in London’s Science Museum. Image – Baruch Coutts Looking at the stars Breguet operated in an era where precision timekeeping was dictated by astronomy, and his workshop, positioned at the heart of Paris’s scientific and commercial networks, was uniquely placed to serve scientists, navigators, and royalty who required accurate solar and mean time readings. Rather than settling on a single method for displaying and correcting the EOT, he explored multiple mechanical solutions, refining some while revisiting earlier ideas when necessary. His approach does not follow a strictly linear evolution but instead reflects a dynamic cycle of innovation, mechanical experimentation, and adaptation. Breguet’s cam-driven system with feeler to indicate EOT, as found in pocke...
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