Calibre UR01 - The Architecture Behind the Rotondo Tourbillon Movement
- Jul 1
- 3 min read
When Refinement and Resilience Share the Same Architecture
Before it became a case, the Rotondo's geometry lived inside its movement, in the Calibre UR01, where the Golden Ratio governs the placement of the main components, bridges, and the shape of its rotor. To understand the Rotondo, one has to start there, at the mechanical core that gave the watch its form.
Proportion as a Starting Point
Developing an automatic flying tourbillon under 4mm is already a rare achievement in fine watchmaking. Doing so while keeping every internal proportion tied to the 1.618 Golden Ratio that also shapes the case structure is a different order of constraint altogether. The position of the UR01's barrel and tourbillon case, its main plate, its oscillating rotor were not fitted into an existing architecture. Thee Golden Ratio proportions and the FIbonacci series principles define its structure to instil a sense of balance, visible both to the eye and on the wrist.
As a result, the calibre measures 3.85mm in thickness and weighs less than 8 grams, complete with central rotor, yet houses 225 components and 29 jewels within that footprint.
Core Elements, Suspended in Balance
At the heart of the UR01, the titanium flying tourbillon cage that houses the balance wheel, completes a full rotation every 60 seconds, freed from an upper bridge so that it appears suspended within the movement.
A suspended mainspring barrel recovers vertical space, delivering a 60-hour power reserve without adding height and reducing weight.
At the back, a solid 18K rose gold rotor turns in concert with the tourbillon, and through the case's sapphire back the two elements read almost as a single choreography of gold and titanium.
Calibre UR01 : Built to Withstand, Not Only to Impress
Thinness and fragility have long been assumed to go hand in hand. The UR01 was engineered to challenge that assumption. Dedicated shock-absorbing solutions protect the movement's most delicate components at both the balance wheel and structural levels, allowing the calibre to sustain shocks of up to 5,000 Gs, a level of resistance uncommon even among far thicker automatic tourbillons.
This resilience is not a late addition to the design. It is embedded in the same architecture that governs the UR01's thinness, proof that at Bianchet, refinement and performance are engineered together rather than negotiated against one another.
Finished by Hand, to the Limit of the Material
A skeleton movement exposes everything and there is nowhere to hide imperfect finishing, which makes every detail matter even more. Each Calibre UR01 is hand-finished in the Bianchet atelier in La Chaux-de-Fonds, Switzerland, with more than thirty hours dedicated solely to the hand bevelling of its bridges.
Every bridge's edge is traced and polished until the metal catches light in a way no machine can replicate, a discipline made considerably more demanding by the choice of Grade 5 titanium, one of the hardest and most unforgiving materials in watchmaking.
Every structural component of the Bianchet calibre is machined in titanium, including the tourbillon cage itself. The cage benefits directly from titanium's reduced mass, placing less strain on the mainspring and contributing to more consistent power delivery. The anti-magnetic properties extend throughout the entire architecture, not as an after-the-fact feature, but as a consequence of how the movement was conceived from the beginning.
Titanium is significantly lighter than steel, corrosion-resistant, and offers a natural resistance to magnetic fields that steel cannot match. For a movement worn daily, in the electromagnetic environment of modern life.
