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MB&F founder Maximilian Büsser has always been a car enthusiast and has taken up the aesthetic characteristics of mid-20th century models in the 2014 HM6 Space Pirate, particularly in subsequent SV "Streamliner" editions. In 2018, MB&F is going even further by presenting one of its most ambitious designs to date.

Horological Machine N°9'Flow' is bold, not only because its shape is unconventional, but also because it requires the use of extremes to achieve it. While the cases in the Horological Machine collection are generally innovative and transgressive, the HM9's case pushes the envelope. Due to its extremely curved curves and sharp angles, new standards and manufacturing techniques had to be explored to obtain a perfectly machined and finished case.

Horological Machine N°9'Flow' was not designed according to the usual production methods. The curves are too pronounced and the finishes too demanding.

When the MB&F team submitted the HM9 drawings to its manufacturing partners, the answer was immediate and unambiguous: impossible to achieve. Other examples, such as the undulating hull of the HM6 Space Pirate, had a complex geometry but the maximum differential height (vertical distance between two adjacent points) did not exceed 5 mm. In the HM9, this differential has been doubled to create the radical curves that give the case a very sensual character.

On these steep curves, the very fine mirror-polished or wider satin-finished strip finishes were problematic: it was difficult to guide tools of predetermined diameter (let us assume 10 mm or more) into the narrow grooves of the case surface. However, there was no question of changing the layout of the different finishes according to the tools, as this would have affected the aesthetics of the HM9 in terms of volume.

The spectacular geometry of Horological Machine N°9'Flow' required equally exceptional contrasting finishes. The requirements of HM9 have therefore led to a change in manufacturing practices.

Given the proportions of the curves on the HM9 housing, it was essential to control the overall size. Measuring no less than 57 mm wide at its widest point, Horological Machine N°9'Flow' required a very compact and yet robust engine. Perhaps the most interesting aspect of the HM9 is to understand how it was possible to combine such an exuberant and expressive design with a small, restrained engine.

The arrangement of the three main parts of the HM9 housing, alternating between a visual flow from widest to narrowest and vice versa, made it impossible to integrate the movement conventionally into a housing with limited transverse symmetry. It was necessary to divide the housing into two axes and design an unprecedented three-dimensional seal. This patented innovation is completely new in the watch industry.

About the HM9 engine

The result of three years of development, the HM9's engine was developed entirely in-house, with the experience accumulated in 13 years of existence (until 2018) and through 14 previous movements.

MB&F collectors and long-time fans will recognize the mechanical pedigree of the HM9 engine. Although presented in a very different form, the double balance with differential is comparable to the Legacy Machine N°2 system. While the LM2 highlighted the purity of design and the amazing effect of its suspended oscillators, the HM9 brilliantly celebrates its expressive design.

The two balances of the HM9 engine are two sources of chronometric data for the central differential that provides the average display. The pendulums are independently driven and spatially separated so that they each oscillate at their own frequency of 2.5 Hz (18,000 A/h). This is an important factor in obtaining a significant average, in the same way that a statistically reliable mathematical average should be derived from separate information sources.

Two pendulums in the same movement inevitably raise the question of resonance, the mechanical phenomenon that maintains a mutual harmonic excitation between two coupled oscillators. Like the LM2 engine, the HM9 engine expressly avoids inducing a resonance effect. It integrates two balances to obtain separate chronometric data that can be transmitted to a differential to produce a stable average display. This objective would not be achieved with two balances oscillating perfectly in phase, providing equivalent chronometric data at all points.

Reminiscent once again of MB&F's Legacy Machine collection, the HM9 features curved arms above the pendulums. The polished appearance of their surfaces creates a striking contrast with the other bridges of the movement.

Technical specifications

HM9 Flow - Technical specifications


Horological Machine N°9'Flow' is available in two versions:

- Road" version with a dial type speedometer;

- Air" version with an aviation-type dial.


Manual winding designed and developed in-house by MB&F

Two totally independent balances with a planetary differential

Pendulum frequency: 2.5Hz (18,000bph)

Single barrel with 45-hour power reserve

301 components, 52 jewels

Hours and minutes displayed vertically


Limited launch editions of 33 pieces each, grade 5 titanium case with a NAC ("Air" version) or pink gold ("Road" version) movement and a limited edition of 18 pieces each, 5N+ pink gold case with NAC movement and rhodium-plated balances ("Air" version) or rhodium-plated movement and 4N pink gold balances ("Road" version)

Dimensions: 57mm x 47mm x 47mm x 23mm

Launch editions: 43 components, pink gold: 49 components

Waterproofing: up to 3 ATM (30m); assembled in 3 segments with patented three-dimensional seal. 

Sapphire crystals

Five sapphire crystals treated with an anti-reflective coating

Bracelet and buckle

Brown hand-sewn calfskin strap with titanium or 5N+ pink gold folding clasp.


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