Unveiled in 2025, Naissance d’une Montre 3 continues to evolve at a rate of two timepieces crafted annually using traditional production methods.
The first timepieces confirm the efficiency of the combined fusee-and- chain transmission system and bimetallic balance, each handcrafted movement being individually certified by the COSC.
A finalist in the “Mechanical Exception” category at the 2026 Grand Prix d’Horlogerie de Genève, Naissance d’une Montre 3 has now established itself as one of contemporary watchmaking’s most ambitious and unique achievements.
In 2025, to mark the tenth anniversary of Chronométrie Ferdinand Berthoud, the Manufacture unveiled the culmination of the Naissance d’une Montre 3 project: a series of 11 timepieces crafted without any digital assistance, using exclusively traditional methods and tools and chronometer-certified by the independent COSC laboratory.
The first timepiece to emerge from this project called for more than 11,000 hours of work. Powered by an exclusive movement combining a fusee-and-chain transmission system with a bimetallic balance, this one-of-a-kind steel timepiece was sold for over 1.2 million Swiss francs at a Geneva auction organised by Phillips in November 2025.
More than 80 artisans and specialists from Chronométrie Ferdinand Ber thoud and Chopard pooled their expertise over five years to bring this one-of-a-kind project to life. A further five years are now required to complete and deliver the remaining ten timepieces. In 2026, the first two models in this series left the Fleurier workshops with the capacity to deliver exceptional chronometric performance. The combination of the bimetallic balance wheel and the fusée-and-chain transmission confirms the relevance of this approach in the quest for precision. The certificate issued by the COSC for the unique steel timepiece auctioned by Phillips confirms these remarkable results.
This performance takes on a very special significance within the context of Naissance d’une Montre 3, in which every component is hand-crafted using traditional methods, without the use of any digital processes.
Upstream, fusee-and-chain transmission
A worthy successor to Ferdinand Berthoud’s No. 3 Astronomical Pocket Watch, the movement of the Naissance d’une Montre 3 has been designed to ensure the most accurate possible timekeeping. It draws on its ancestor’s aesthetic codes but above all on its fundamental mechanical principles: the fusee-and-chain mechanism, the specific bridge structure, diamond shock absorbers and a regulating organ featuring a split bimetallic balance.
The purpose of the fusee-and-chain device is to transmit as constant a supply of energy as possible to the oscillator. To achieve this, the cone-shaped fusee compensates for the gradual decrease in torque delivered by the mainspring by increasing the lever (moment) arm as the tension in the chain decreases. When the movement is fully wound, the chain is completely wrapped around the narrower end of the fusee and the mainspring delivers its maximum power. As the latter unwinds, the chain gradually winds onto the barrel drum, moving from the smaller to the wider diameter of the fusee. The variation in this component’s diameter then compensates for the decrease in torque at the mainspring.
A Breguet-type stopwork mechanism has been fitted at the top of the fusee to ensure only the optimal range – meaning neither too high nor too low – of the mainspring’s torque is used. Ultimately, this translates to just four turns of the barrel out of a total of approximately 8.5 turns. Combined with the core principle of fusee-and-chain transmission, this limitation ensures that the escapement is supplied with extremely consistent energy.
Furthermore, the Naissance d’une Montre 3 model features an auxiliar y spring integrated into the fusee, which maintains the transmission of energy to the balance-spring during winding (crown position 2).
Downstream, the oscillator and its “Guillaume” -type bimetallic balance
The oscillator is the second chronometry-oriented device in the Naissance d’une Montre 3. It is based on a “Guillaume”-type bimetallic balance designed to compensate for the thermal variations affecting the steel balance-spring.
Comprising two bimetallic half-rims (also known as fellies) deformed by temperature changes, this type of balance compensates for variations in the balance-spring’s rigidity by altering its moment of iner tia. Invar is a material meticulously selected for its extremely low coefficient of thermal expansion and when combined with brass, it profoundly alters the thermomechanical behaviour of the bimetallic balance in order to compensate for the primary error and eliminate the secondary error. (See the “Keen to know more?” section)
With the development of elasticity-stabilised alloys used in the majority of modern balance-springs, this type of bimetallic balance gradually gave way to self-compensating balances, leading to the loss of the associated exper tise. Returning to the essence of classic regulators from a century ago thus required a lengthy period of research, testing and learning in order to master a reliable and reproducible traditional production method.
Chronométrie Ferdinand Ber thoud has thus literally re-established this lost expertise, in keeping with the objectives of the Naissance d’une Montre programme. This endeavour nonetheless encountered significant technical difficulties, par ticularly relating to the quality of the metallurgical bond between brass and the Invar alloy, as well as issues relating to porosity and material degradation.
Once this technique had been mastered, the teams rediscovered the impor tance of a forgotten process: hammering the brass after casting. This crucial stage increases the metal’s yield strength, guarantees the stability of its thermal properties, as well as ensuring the reproducibility of the balance’s behaviour.
Following the challenges associated with craf ting the bimetallic balance, its adjustment constitutes an equally essential stage in the Naissance d’une Montre 3. Unlike modern regulating organs whose thermal characteristics are predetermined at the time of their production, it is the watchmaker’s own responsibility to set and adjust the thermal coefficient of a bimetallic balance. Achieved by finding a delicate equilibrium between the balance’s geometry, its weight distribution and the characteristics of the balance-spring, this adjustment requires par ticularly specialised expertise. Movable weights positioned on the half-rims thus enable accurate fine-tuning of the balance’s thermal coefficient, ensuring optimal chronometric per formance under varying temperature conditions.
To validate this chronometric per formance individually, ever y Naissance d’une Montre 3 movement undergoes testing by the Of ficial Swiss Chronometer Testing Institute (COSC). The results obtained from the first timepiece of this project confirm the effectiveness of the two mechanisms at the hear t of the watch: the fusee-and-chain transmission system and the bimetallic balance.
Three figures par ticularly illustrate this per formance:
• The average daily rate in the various positions is 0.91 s/day
• The rate variation per degree Celsius is 0.01 s/day/°C
• The rate correction, i.e. the watch’s ability to return to its nominal rate after a disturbance, is 0.69 s/day
Naissance d’une Montre 3 is also among the finalists for the 2026 Grand Prix d’Horlogerie de Genève in the Mechanical Exception category.
Keen to know more?
Temperature-dependent timekeeping stability was one of the fundamental challenges facing precision watchmaking in the 18th and 19th centuries. Watchmakers such as Pierre Le Roy, John Arnold and Ferdinand Berthoud worked on solutions designed to alter the inertia of the balance at varying temperatures, in order to maintain a constant rate of oscillation. It was against this backdrop that the bimetallic balance was developed and gradually established itself as the standard solution, making it possible to correct what is now referred to as the primary error.
However, as early as 1775, Ferdinand Berthoud observed that this compensation is accurate only at two distinct temperatures selected during adjustment, such as a very low temperature and a very high temperature. At intermediate temperatures, the watch tends to run fast, whereas below the first temperature or above the second, it runs slow. This phenomenon is now known as the secondary (middle-temperature) error or Dent’s anomaly, which was studied and formalised in the 19th century by London-based watchmaker John Edward Dent.
It was not until the early 20th century, with the work of Charles-Édouard Guillaume – a native of Fleurier and winner of the 1920 Nobel Prize in Physics – that a solution to this problem was found. He invented and developed the concept of the bimetallic balance, known as the “integral” or “Guillaume” balance, that was made possible by the discovery of new alloys with very low thermal expansion – and notably Invar 42. The thermal deformation of the balance was then adjusted not only to compensate for the primary error associated with the balance-spring, but also to reduce the non-linear element responsible for the secondary error.
