On the Quest for Constant Force: Ferdinand Berthoud Chronomètre FB 2RE

Ferdinand Berthoud († 1807) was regarded as one of the great watchmakers of his time and was at the forefront of the development of modern marine chronometers. His naval watches helped French ships to new shores in the 18th century (which earned Berthoud the title “Clockmaker and Mechanic by appointment to the French King and Navy”) and his literary legacy helped generations of future watchmakers at the workbench.

In 2015, the “Chronométrie Ferdinand Berthoud” brand was founded by Chopard’s CEO Karl-Friedrich Scheufele to keep Berthoud’s legacy alive. After winning two GPHG Awards in 2016 (Aiguille d’Or) and 2019 (Chronometry), the young watch brand now presents another highlight: Ferdinand Berthoud’s first ever round watch, which is brimming with complications.

Mechanical Watches and the Problem of Constant Force

Generally, most mechanical watches are powered by the wound mainspring in the barrel, which transfers its power via the gear train to the escapement. The problem, however, is that this power transmission is not constant, since a fully wound spring naturally transmits more power to the gear train than a mainspring in a relaxed state. This in turn negatively affects accuracy.

For centuries, watchmakers have been working on a solution for constant power transmission – something like the holy grail of watchmaking if you will – to compensate for the successive loss of tension in the spring. With the new Chronomètre FB 2RE, Ferdinand Berthoud has installed two such mechanisms, which were developed for precisely this purpose.

Fusée And Chain

Particularly efficient and visually impressive, although not exactly space-saving or easy to implement, is a continuously variable transmission between the mainspring barrel and gear train called the “fusee and chain system”.

When the watch is fully wound, the chain is completely wound on the fusee. Now, if the spring tension of the watch slowly decreases (meaning the power reserve shrinks), the chain with its 790 individual parts in the case of the FB 2RE unwinds slowly from the conical fusee in the direction of the barrel from top to bottom. In doing so, the chain moves on the fusee from the smaller to the larger diameters.

Ultimately, it is exactly this slowly increasing diameter of the fusee that compensates for the decreasing torque of the mainspring. The result is an almost constant power transmission and therefore a higher precision.

Remontoir d’Égalité

In addition to the fusee-and-chain transmission, Ferdinand Berthoud has also built in a remontoire. Its underlying idea remains unchanged: To counteract the decreasing tension of the spring, so that it does not matter whether the watch has just been wound or is about to run down. However, the remontoire not only repeats the effect of the first complication, but rather works in a complementary manner, since it acts at a different point in the movement.

While the fusee compensates for the torque transmitted to the gear train and thus maintains the amplitude, minimal irregularities also occur when the gear train teeth mesh. Here, the remontoire, which is attached to the escapement’s escape wheel, comes into play. A second, small spring feeds in just enough energy every second to sufficiently compensate for this transmission loss.

What About the Rest?

As you would expect from a Ferdinand Berthoud watch, also the rest of the Chronomètre FB 2RE is as good as it gets in terms of finishing and refinement. The dial of the 44mm watch is made of Grand Feu enamel (more on this here) and also for the other components Ferdinand Berthoud relies on its own craftsmen and traditional tools. Especially small particulars, which other luxury brands like to rationalize, are a joy to behold: The intricate matt bridges of the symmetrical movement are made of German silver, the balance cock is arrow-shaped and the hands are made of blued, 18-carat white gold. It’s all about the details.

Price & Availability

The Ferdinand Berthoud Chronomètre FB 2RE is limited to 20 pieces – 10 in white gold and 10 in rose gold – and sets you back CHF 210,000 (just under EUR 195,000).

More information at Ferdinand Berthoud.