Fantastic Calibers and Where to Find Them: De Bethune Caliber DB2109V4 in the DB25 Starry Varius Aerolite

We’ve talked in-depth about some of the more iconic creations from this era in independent watchmaking – timepieces like Urwerk’s UR-103, and Akrivia’s AK-06. It’s now time to turn our attention to the beating heart of the tradition – movements. 

While design and material science innovations may catch our eye with greater ease, the most creative watchmakers often express themselves through mechanics. The best in the craft are fundamentally problem-solvers, pushing the watchmaking tradition forward by resolving long-known technical issues or inventing new means of moving energy from mainspring to escapement. 

Today, we’re focusing on De Bethune’s caliber DB2109V4. Found in the DB25 Starry Varius Aérolite, this caliber is a great representation of Denis Flageollet’s relentless pursuit to push the craft of mechanical watchmaking into the 21st century. Before we dig into Flageollet and De Bethune’s contributions to watchmaking, let’s first cover the basics of the timepiece and its caliber. 

DB25 Starry Varius Aérolite & Caliber DB2109V4

The DB25 Starry Varius Aérolite is all things De Bethune in a single timepiece. It’s clearly connected aesthetically to the history of watchmaking with its large, Roman numerals and mirror-polished Breguet hands. The timepiece’s dimensions and overall profile provide it with the cover of a “low key” watch. But upon closer inspection, the meteorite dial and concealed tourbillon movement are thoroughly modern.

Winner of the 2018 GPHG Award for chronometry, the in-house caliber DB2109V4 is about as technically sophisticated as exists. With a high-frequency (5Hz or 36,000vph) thirty-second tourbillon, self-regulating double barrel, blued titanium balance with white gold inserts, simplified dead-beat seconds – all patents by the brand – this movement can be viewed as the culmination of Flageollet and the De Bethune team’s chronometric pursuits spread across 20+ years. The DB25 Starry Varius Aérolite is a bridge between past and future on both aesthetic and technical levels.  

While the DB28 is an undisputed icon in independent watchmaking and the flagship timepiece for De Bethune, the DB25 Starry Varius Aérolite sticks out for a few reasons when examining Flageollet and the De Bethune team’s technical contributions to watchmaking. Namely, it features nearly the entire catalog of the brand’s patents, from its 2003 patented hairspring with a flat terminal curve all the way through 2016 with its titanium balance wheel with white gold inserts.

“As the great artists of previous centuries have shown in their chosen fields, the creative process is inspired by its time; it builds on it and is a reflection of it. However, being of one’s time does not necessarily mean representing more or less faithfully what is en vogue. You can choose disruption or continuity, to transgress or to transcend established rules …” – Denis Flageollet, Horological Alchemy 

De Bethune’s contributions to watchmaking history

In Horological Alchemy, Flageollet’s deep dive into his watchmaking philosophy, he makes it clear that he is a traditional watchmaker, even when De Bethune’s aesthetic and technical innovations are the definition of modern watchmaking. Years and years of experiments and pursuits with mechanics and materials, everything ultimately serves chronometry. That is where it starts. That is where it ends.

So an overview of Flageollet and the De Bethune team’s contributions to watchmaking history, as seen in the DB25 Starry Varius Aérolite, is focused primarily on chronometric innovations. 

2003, the De Bethune flat terminal curve balance spring

There was roughly a two century period where the balance spring was considered optimized. A done deal. To be fair, it takes a very courageous individual to work on optimizing such an established component in watchmaking. Yet, that is the origin of De Bethune. The brand’s earliest patent from 2003 is its hairspring with flat terminal curve. Found in the DB25 Starry Varius Aérolite, the flat terminal curve balance features a significant reduction in the balance spring’s height (an important element in placing the balance on the dial side of many De Bethune timepieces).

DB25 Starry Varius showcasing the flat terminal curve balance spring and titanium with white gold insert balance wheel.

2016, titanium with white gold insert balance wheel 

No surprise that the first invention centered on the balance spring and the second on the balance wheel. Fascinating here is that the original invention of a chronometrically-optimized titanium and platinum balance wheel has been upgraded continuously. Flageollet and De Bethune have executed eight more improvements to the original balance wheel, beginning with the first in 2004 to its latest in 2016. Titanium, white gold, palladium, silicon: fundamental research on materials has also entailed research into temperature changes. 

Experimenting with material and balance weights is a major part of never-ending work on sensitivity to magnetic fields, inertia, aerodynamics, efficiency, and reliability.

In the DB25 Starry Varius Aérolite, the caliber features the latest in the brand’s pursuit of chronometric excellence with the 2016 patented titanium balance wheel with white gold inserts. On one hand, these pursuits may seem extremely pedantic (what isn’t in watchmaking?). On the other though, the exploration of balance wheel performance has led to a significant boost to power reserves. Regularly sporting 5-day power reserves on manual-wind timepieces, few brands offer such consistently long power reserves.

DB28 XP Tourbillon

The world’s lightest tourbillon 

We’ve come a long way since the invention of the tourbillon by Abraham-Louis Breguet at the start of the 19th century. Then, the complication was used to ensure chronometric performance in pocket watches. Today, the wristwatch experiences a series of swift motions in day-to-day life that the origins of the complication never endured. Keeping the spirit of the tourbillon alive, the De Bethune solution to everyday wrist usage was to increase the frequency and rotational speed. Both ensure that the constant motion in wear does not significantly impact chronometry. 

Of course, anything that pulses and rotates faster requires a huge drop in weight. Otherwise, powering a standard weight tourbillon at a higher speed would be overly costly to the power reserve. Flageollet and De Bethune’s solution is the world’s lightest tourbillon cage, weighing a mere 0.18g (about 1/10 the weight of a metal paper clip). Held together by 63 components and spinning every thirty seconds, rather than the traditional sixty, it’s mesmerizing to observe on the Starry Varius Aérolite. This contribution to watchmaking is probably the one that goes the most against the grain of popular perceptions of De Bethune – it’s not common to place the tourbillon at the top of the brand’s inventions. There is a strong argument that Flageollet was one of the first to begin conceptualizing and creating the modern version of the most traditional complications in mechanical watchmaking. 

These three technical contributions found in the DB25 Starry Varius Aérolite fly beneath the radar. The brand’s most well-known innovations revolve around what is arguably more immediately useful and accessible – the ultra-ergonomic floating lug system in the DB28 or maybe even the triple pare-chute shock absorbing system that safeguards the balance wheel from everyday wear. 

Our view is that recognizing the breadth of Denis Flageollet and De Bethune’s brilliance and importance requires a strong focus on pure mechanical watchmaking. The DB25 Starry Varius Aérolite underscores the bundling of technical innovations that are spread across roughly two decades of fundamental research in watchmaking. It’s the coming-together of many different experiments, some related and some unrelated.