e Bethune’s avowed ambition is to lastingly—an important word—improve the timekeeping precision and reliability of a mechanical watch that is subject to constant and erratic wrist movements. The chronometric performance of a timepiece at a given point in time is one thing; guaranteeing its stability in real-world conditions, which vary considerably from one user to another, is something else entirely. In laying the foundations for what it calls chronometry for the twenty-first century, De Bethune has rolled out a succession of technical advancements: a balance spring with a flat terminal curve; new-generation balance wheels; innovative shock-absorbing systems and continuous improvements to the escapement.

These key parameters, interacting one with the other, oblige De Bethune to constantly rethink movement architectures and the geometry of components, harnessing avant-garde techniques and employing contemporary materials. Indeed, Denis Flageollet grounds his practice in watchmaking’s “grand tradition” which, as he is quick to point out, “has always been innovation”—that of the great watchmakers of the classical period, who were the innovators of their day.

The quality factor

Optimal chronometry requires maximum quality. This can be achieved through a higher moment of inertia for the balance wheel combined with reduced overall mass. De Bethune embarked on this ongoing quest for balance wheel optimisation and, consequently, chronometric precision and stability in 2004. Through progress in materials—successively titanium/platinum, thermo-compensated silicon, silicon/platinum, silicon/palladium, silicon/white gold then titanium with white gold inserts—and specific geometries and finishes, De Bethune has consistently devised and improved its balance wheels.

In its optimal form, incorporated into movements as of 2016, the De Bethune balance wheel comprises a lightweight titanium core with white gold weights around its rim that distribute mass to the periphery. Combined with optimised ergonomic profiles and high-level finishing, this increases the moment of inertia while limiting overall mass, reduces friction and sensitivity to external disturbances, and stabilises amplitude, while its aerodynamic form prevents suction effect.

At the same time as it was working on its balance wheel, De Bethune developed a balance spring whose optimal concentric breathing improves the isochronism of the balance wheel/balance spring during wrist movements and in different positions. The key was to replace the traditional Breguet curve with a flat terminal curve. Designed for enhanced shock absorption and to significantly reduce deformations caused by impacts, it increases the oscillator’s stability and maintains frequency. These factors result in better real-world performance and, equally importantly, the balance spring can be fitted without further adjustment.

Shock-absorbing system

To further improve shock-resistance, De Bethune has developed a three-point shock-absorbing system, mounted on spring-blocks, which protects the heart of the watch by reducing external influences. This triple pare-chute system comprises a titanium bridge fitted with shock-absorbing jewels at each end, paired with spring blades and a central shock-absorber. By providing axial and radial support, this unique construction stabilises the balance’s amplitude and consequently its chronometric precision.

Silicon escape wheel

De Bethune has used a silicon escape wheel in its escapements since 2009. Silicon halves the risk of wear to the lever’s pallet stones. Additionally, the shape of the escape wheel’s teeth is designed to reduce friction, minimise inertia and create profiles that facilitate the smooth sliding of surfaces that come into contact.

This lighter escape wheel, which uses less energy when starting and stopping, combined with a specific pallet shape reduces the force of impacts and considerably improves the escapement’s efficiency.

Sensorial Chronometry Project

Introduced in 2022 and the first of its kind, the purpose of the Sensorial Chronometry Project is to precisely adjust a watch according to its wearer’s lifestyle and habits. Nothing less than customised chronometry. For two weeks, the customer wears a lab watch. Packed with sensors, it tracks their movements and also measures factors such as positions, shocks, ambient temperature, humidity and atmospheric pressure that are specific to the person’s lifestyle and environment.

Collected data is analysed at De Bethune’s chronometry workshop, where the customer’s finished watch is tested in an atmospheric chamber that reproduces their environment, on a robotic arm that replicates their movements. The watch is then precisely adjusted in six positions to actual conditions of use. Based on the most frequently adopted positions, even the most common ambient temperatures, dynamic balancing and rate adjustment (fast or slow) can be fine-tuned by very slightly “unbalancing” the balance wheel or recentring the balance spring.

This dynamic certification goes beyond conventional static certification. It enables adjustment—hence precision—that is customised to the future owner’s lifestyle and the daily constraints of their environment.

In-house balance-spring production

In another recent development, De Bethune has brought balance-spring production entirely in-house. Wire drawing (using 30 separate draw plates to obtain the required diameter), rolling, coiling, heat treatment, colleting, forming the outer curve, assembly with the balance wheel (also produced in-house) and final adjustment are now carried out at the brand’s balance-spring workshop.

Such a considerable effort reinforces De Bethune’s independence; it also responds to technical considerations. “The idea is to go all the way with our concept,” Denis Flageollet told us. “Externally sourced balance springs comply with standards that are based on averages and don’t allow us to adjust their dimensions as finely as possible to match our balance wheels. Now that we master every stage, we can act on variables at micron level, in terms of the spring’s thickness, starting height or the radius of the inner curve, and adapt its geometry to its balance wheel. And a few microns here and there help us push the boundaries of our chronometric precision even further.”

In Denis Flageollet’s mind, chronometric precision is a “never-ending quest”. The Résonique project, launched in 2012, is proof. This fundamental research into high frequency focused on silicon springs to prevent friction in the balance-wheel pivots, using a magnetic rotor and an acoustic oscillator. Flageollet admits that the project “didn’t meet all its objectives” but confirmed his belief that "mechanical watchmaking will make further gains in precision through ongoing research into the balance wheel/balance spring we inherited from Huygens, 350 years ago.” A never-ending scientific quest, indeed.