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Inside the MB&F HM9 Flow

With many of its previous horological machines already cruising through the time/space continuum, MB&F’s HM9 Flow has to travel light years to catch up to its forebears. But, since the HM9 Flow is essentially a jet engine, it will undoubtedly reach the MB&F HM4 Thunderbolt and the MB&F HM6 Space Pirate very soon.

Launched just a few months ago from deep within the bowels of MB&F’s Geneva HQ, Horological Machine No.9 Flow clearly recalls aeronautic jet propulsion with its two satin-finished air scoops seamlessly mounted alongside two balance wheels ensconced in sapphire-topped pods. Between them, the movement’s prominent (and unusual) planetary differential gear ensures that the dial, showing hours and minutes, remains precise, even though the dial is set at a 90-degree angle to the movement.

Of course, MB&F is well versed in creating time machines that seem to defy gravity and the laws of physics. But this latest watch demonstrates that MB&F founder Maximilian Büsser also frequently battles with watchmaking convention. Because of HM9’s unusual aerodynamic shape, Busser and Friends needed to divide the 57mm-wide titanium case along two axes and devise an unprecedented three-dimensional gasket for the watch.

MB&F CEO Maximilian Büsser

“Our own MB&F engineers initially said the whole project was not feasible – for one because there is no way such a design could be made water resistant,” explains Büsser. “Six months later, they had worked with our gasket manufacturer to create the first-ever 3-D water-resistance gasket. It may seem like a little detail, but it is an incredible step forward for contemporary watchmaking.”

This patented innovation, a world premiere, makes the HM9 case water resistant to thirty meters.


The engine within this dramatic case took two years to develop. It could very likely only have been devised by the team that has created fourteen unusual movements, at least one of which (Legacy Machine No. 2) also utilized a double balance paired with a differential.

“The movement development went pretty smoothly, even though it took over two years, but that’s because we had already spent three years experimenting on the double escapement movement with Legacy Machine No.2 and conical gears on HM6. If that had not been the case, I cannot even imagine how many years this project would have taken,” Büsser adds.

The unusual case, on the other hand, did threaten to scuttle the entire HM9 entirely.

“The two “teardrop” sapphire domes on the case nearly killed the whole project a few months before launch date. It was terrifying.” Busser admits. “The sapphire manufacturer had a rejection rate of more than seventy-five percent on each piece, after having spent sixty to eighty hours machining and polishing them. Finally we managed to get some pieces trickling out, but production is therefore not at all where we were expecting.”

He adds that initially all MB&F case makers turned down the HM9 project, calling it either too difficult or impossible.

“Finally a small and young manufacturer took on the project – he sort of regretted it later on, as the qualitycontrol rejection rate is more than fifty percent,” he notes.


Double escapements are rare in watchmaking, in part because the watchmaker requires perfectly executed engineering, seamless machining and extremely high tolerances – especially when creating a differential gearing system.

Unlike other multi-balance movements, the HM9 engine deliberately avoids a resonance effect (a type of harmonic mind meld among two linked oscillators) in favor of a system using the two balance wheels to obtain “discrete sets of chronometric data” translated by the differential to produce one stable averaged reading. The balances are individually impulsed and separated to ensure that they beat at their own independent cadences of 2.5Hz (18,000 bph) each.

Echoing earlier MB&F’s Legacy Machines, HM9 utilizes dramatic polished and curved arms to hold these dual balances. Here their placement is almost as critical as the aerodynamic design to the HM9’s architecture, though the bridges are possibly less surprising than they were when we first discovered them in the earlier MB&F watches. The polished arches also serve to contrast with the finish of the movement bridges below.

Getting the chronometry perfect is just as important to Büsser as the overall watch design.

“We need to respect our core values,” Büsser says. “We are above all engineers and watchmakers. The wild creativity must not hinder our quality and performance.”


While many MB&F watch designs echo mid-20th century aviation or automotive profiles, Büsser explains that his designs rely far more on his own personal experiences.

“At the beginning of a project, I don’t actually think: “Let’s create a timepiece that looks like a car or a plane,” he says. “I create a piece that gets my adrenaline flowing and then, when the design is finalized or when I have the first 3D print on my wrist, I realize where the influences stem from. Coco Chanel was credited with a saying I love: “He who insists on his own creativity has no memory.” Everything that has seeped into me for the last fifty-one years is the base for the creative outflow.”

Sometimes, an initial design idea undergoes substantial alteration before the final version is realized. For the HM9 however, the final design was surprisingly true to Büsser’s initial idea.

“I am so proud of the team because the final piece is practically identical to my initial concept design,” Busser says. “That usually never happens. I guess either the engineers were even smarter than usual, or I was just more difficult and adamant not to allow modifications.

MB&F’s latest Horological Machine, No. 9 Flow, exhibits a kinetic aerodynamic shape that, with judicious polish and satin finishing and dramatic sapphire windows, nicely frames a technically exacting engine. Flow fits perfectly into this independent maker’s ongoing series of retro-futuristic time machines.

The HM9 is offered with a choice of two finishes: an ‘Air’ edition with darkened NAC movement and aviation-style dial, and ‘Road’ edition with a rose gold-plated movement and a speedometer-style dial.

MB&F in 2019 will release the final version of the HM6 Space Pirate, plus two new movements that Büsser says will be unusual, even for MB&F.

“And we have gotten out of our creative comfort zone,” he says. “Yes, it may seem weird, but we actually have a creative comfort zone. We explore new unchartered territory, which actually scared the hell out of me!” Each of the two MB&F HM9 Flow editions, Air and Road, will be made in titanium cases and limited to 33 pieces each. Price: $182,000.

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