The Tourbillon (derived from the French word for whirlwind) is one of the most poorly understood complications for the average watch collector. If you have seen a tourbillon for sale, you may have learned two things: they are expensive, and they are frequently in larger watches. Let’s explore this complication and see if it still has a place in modern horology.
As is the case with many elements of modern watchmaking, the idea and patent behind the tourbillon traces back to the father of modern horology, Abraham Louis Breguet in 1801. When regulating a watch, they frequently perform differently in different positions. In creating the tourbillon, Breguet was trying to ensure a movement would perform similarly in all of the vertical positions - crown up, crown down, crown left, and crown right.
He postulated that you could minimize the variation in each of these positions if the critical parts of the movement rotated inside of the watch. In a given minute, the escapement will spend equal time in those four positions.
This mechanism is shown below by the Bulgari BVL150, the smallest tourbillon currently produced. We have highlighted the outside of the tourbillon cage in red. Inside that cage, the balance wheel oscillates, the pallet fork actuates, and the escape wheel slowly rotates. All the while, that cage is making (generally speaking) one rotation every 60 seconds.
The record-setting Bulgari BVL150, the smallest tourbillon movement of modern production.
Having covered the theory and mechanism, the natural question becomes: is it worth it in today’s world? From a pure timekeeping perspective, most likely it is not. A well regulated modern movement is almost always more accurate than a tourbillon. This accuracy is owing to several primary reasons.
First, powering this operation is quite a task. It generally takes a more powerful mainspring in order to fuel this movement and places additional wear on the complex parts of the escapement. Over time, this can contribute to reduced accuracy and reliability.
More importantly, the positional accuracy fluctuations are no longer quite the problem they once were. In Breguet’s time, the balance wheel was a split wheel mechanism constructed of two different metals. The bi-metallic construction was to assist the movement with accuracy across a wider range of temperatures.
A vintage bi-metallic balance wheel
Modern balance wheels are composed of a single type of metal and are more rotationally balanced. The creation of a beryllium, copper, and iron alloy called Glucydur eliminated the need for bi-metallic split construction. As such, different positions are less likely to impact overall accuracy.
Additionally, this mechanism was devised for pocket watches, which generally reside upright in a fixed position. With a wristwatch, however, natural wrist movements put the movement in a number of different positions throughout the day.