What happens when you take Abraham-Louis Breguet’s tourbillon and tilt it?

In Episode 3 of Masters of Chronometry, Wei Koh and Constant Kwong trace one of the most fascinating and misunderstood branches of the tourbillon’s evolution: the inclined tourbillon.

The story begins with a fundamental problem. A conventional tourbillon was conceived to average positional errors while a pocket watch sat vertically. But watches do not remain in one orientation. What happens when the watch is laid flat, held at an angle or, eventually, worn on the constantly moving wrist?

The answer first appeared in America in the 19th century with Andrew Holden Potter, a Boston watchmaker whose extraordinary inclined-balance tourbillon would spend much of its history confused with the work of another American watchmaker, Albert Henry Potter.

Around seven decades later, Walter Prendel took the idea dramatically further. Trained at the German Watchmaking School in Glashütte under Alfred Helwig, Prendel created an extraordinary six-minute tourbillon in which the escape wheel, pallet fork and balance were progressively inclined at different angles. Thanks to the generosity of its current owner, Revolution is able to show this remarkable historical watch in detail.

The story then enters the modern era with Robert Greubel and Stephen Forsey. Their Double Tourbillon 30° translated the principle of inclination into the wristwatch and went on to demonstrate its chronometric validity, scoring 915 out of 1,000 points at the 2011 Concours International de Chronométrie.

From there, Wei and Constant explore Greubel Forsey’s Tourbillon 24 Secondes and Tourbillon Cardan, the work of Éric Coudray, the HYT Conical Tourbillon, Jaeger-LeCoultre’s Heliotourbillon and, most recently, ArtyA’s Complexity with its two inclined Cônillon tourbillons connected by a differential.

From a nearly forgotten Boston pocket watch to some of the most technically ambitious wristwatches being made today, this is the story of more than 165 years spent asking one deceptively simple question: what happens when you put the tourbillon at an angle?