Twenty-twenty-four marked Greubel Forsey’s 20th anniversary, an occasion celebrated with their first chronograph, the Nano Foudroyante EWT. The brand’s tenth “Fundamental Innovation” since its founding back in 2004, the Nano Foudroyante EWT is a flyback chronograph with a flying tourbillon and an independent micro-scale lightning seconds, or foudroyante.

The watch marked many firsts for the brand. Aside from being Greubel Forsey’s first chronograph, it is also the brand’s first flying tourbillon – noteworthy given its longtime focus on the tourbillon. Despite its extensive history with innovative tourbillon constructions, Greubel Forsey (GF) has never before created one with a flying architecture. 

Initial thoughts

GF is often regarded as among the best in terms of innovative watchmaking and artisanal chronometry. Although the brand’s styling can arguably be too much at times, its core signature of high-end horology is unmistakable and defined by exemplary finishing and exceptional engineering in equal measure. 

The Nano Foudroyante EWT is interesting in many respects. The combination of complications is unusual, even for GF, and feels like more of a conceptual platform to present the “nano” sized lightning seconds (that runs independently of the chronograph). That said, execution is typical of GF in being high quality all around. It is a perfect example of the brand’s approach to watchmaking, both decoration- and engineering-wise.

Similarly, the aesthetics of the dial and case are recognisable as GF, since they employ elements found in other models. While the execution of the dial and hands are top quality as expected, the design feels a little too plain, with the dial resembling something of a prototype rather than a finished design.

That said, the Nano Foudroyante doesn’t feel like a conventional GF, being the smallest watch ever made by the brand, which is historically known for its oversized watches. In fact, the just-under-38 mm case feels almost vintage-inspired, especially with its domed “box” crystal — which can’t really be said for any other GF creation. The Nano Foudroyante does feel like a GF watch though, because it is still hefty and dense, despite the smaller size.

More broadly, the watch reiterates the mechanical philosophy of the brand; it contains concepts that can only come from the minds of great watchmakers. A watch reinforces the brand’s pivot away from oversized sports watches and back to high-end horology, indicating that GF has finally got back its bearings.

The Nano Foudroyante EWT is also typical GF in another respective – it is expensive. With a retail price of almost half a million Swiss francs, it is amongst the most expensive watches of this type on the market, even taking into account the complications and quality.

Why make something so over-engineered and expensive that is not all that useful in itself? The answer likely lies in the fact that the Nano Foudroyante EWT is less a watch for the catalogue but arguably a proof of concept for the micro-gear mechanism, which might be further refined and extended to the going train or regulator, making way for exceptionally energy efficient movements with ultra-long power reserves.

Micro- to nano-mechanical

EWT is short for “Experimental Watch Technology”, a research and development programme inside GF seeking to reinvent familiar watchmaking concepts and mechanisms. 

One of its earlier endeavours was miniaturising components to an almost nano scale, with the goal of reducing energy consumption. The first prototype with a “nano” foudroyante hand was presented in 2017. Traditionally a foudroyante hand — which travels at a rapid one revolution per second — is geared to the escape wheel and ends up consuming a large quantity of the mainspring’s energy, resulting in an impractically short power reserve.

EWT scaled down the components of the foudroyante, reducing its energy consumption. That said, the components are still large enough to be handled by tweezers. “Nano” refers rather to the energy consumption, rather than pointing to actual nanoscale technology — which is measurable only in billionths of a metre.

Composed of parts made via LIGA lithography, the micro-mechanical concept that debuted in 2017 has now been implemented in the Nano Foudroyante EWT, albeit with a different execution. 

Since the balance runs at 3 Hz, the escapement unlocks the escapement twice per oscillation making for six ticks per second. The actual speed of the escape wheel can’t really be determined since it depends on its number of teeth, but is much slower than one revolution per second. 

Extracted from EP4428622A1

European patent EP4428622A1 illustrates the internal structure of a possible incarnation of the flying tourbillon cage. There is a small pinion on mobile 25 engaged with a large diameter wheel 21 co-axial with the escape wheel. Mobile 25 itself is then engaged with a gear 27 which carries the foudroyante hand.

The transmission ratio between the escape wheel and the assembly of gears is what makes the lightning seconds hand to race forward six times a second, completing a full revolution.

GF claims that the micro-scale of EWT reduces the energy consumption of a classic foudroyante by a factor of 1,800. And at the same time, a 90% reduction in volume compared to said mechanisms. The patent, however, shows the structure comprises of many components which should generally generate some important losses, to friction for example.

If GF’s claim holds true and the foudroyante only consumes 1.6 nanoJoules per tick, then the extreme miniaturisation of components really is a viable way of creating more energy efficient mechanical timepieces in the future. Fewer energy losses are desirable in any mechanical system; in the case of a watch that would translate into longer power reserves and even enhanced accuracy. 

The foudroyante in the Nano Foudroyante EWT runs constantly since it is directly linked to the escapement. As it theoretically consumes negligible amounts of energy, its nonstop motion should have no impact on chronometry.

With the chronograph running and the foudroyante hand speeding around the dial, the watch has a short 24 hours of “chronometric” power reserve, meaning it stays stable and within chronometer specifications (although the piece isn’t officially certified by COSC or other such authority). 

Considering the experimental nature of the Nano Foudroyante EWT, the single-day power reserve is acceptable, but it will presumably be lengthened with further development of the concept. For a piece built around an energy-efficient system, just 24 hours of power reserve is too short. 

A bundle of complications

The name of the Nano Foudroyante EWT might be misleading: the watch is much more than just the tiny lightning seconds indication. Packaged in the small, 37.9 mm case – arguably tiny by GF standards – is an integrated chronograph movement with a flying tourbillon regulator that also carries the discussed foudroyante on its cage.

The appearance of it all is certainly restrained. The case is simple in shape, but finished well. The case middle is white gold while the bezel and back are tantalum, making for a pleasantly weighty timepiece for its size.

Aside from the compact case, the dial is bright and silver, with simple markings. The typical GF typeface and sword hands are present, along with the asymmetric layout that has become characteristic of the brand. 

Given the small diameter of the dial, the flying tourbillon dominates the watch face, its large cutout located somewhere in-between five and six o’clock. The tourbillon doesn’t resemble a conventional tourbillon, since neither the free-sprung balance nor the cage are prominent.

Integrated “lightning” seconds

Instead, taking centerstage is the sub-dial for the foudroyante, which is actually mounted on the tourbillon cage, above the balance. The lightning seconds hand completes one revolution a second, while the eccentric lightning seconds sub-dial makes one revolution a minute along with the tourbillon cage. While this parallel axis rotation advances, the seconds sub-dial maintains its vertical orientation relative to the rest of the dial, creating the optical effect of a floating register.

Although it looks like some differential gearing is at play, the cited patent suggests the differential effect is in fact achieved through gearing the sub-dial to the escape wheel as well. This means that the escapement powers both the foudroyante hand and its dial — which is nothing short of amazing considering GF’s claim of just 1.6 nanoJoules per tick of energy consumption. 

The level of mechanical mastery required to implement this kind of additional gearing on a flying tourbillon cage can’t be overstated. Due to their construction, flying tourbillons are usually executed with very lightweight cages, as not to impose too much stress on the single supporting pivot.  

The large cage, with its additions, not only adds weight, but also a degree of complexity. Unsurprisingly, the tourbillon assembly alone comprises of a staggering 142 pieces — equivalent to an entire simple time-only movement.

Unconventional chronograph

While the tourbillon-foudroyante is the central element of the movement, the calibre also incorporates a flyback chronograph. In its 20 years of existence, GF has launched double and quadruple tourbillons, a perpetual calendar, and even a grande sonnerie, but never a chronograph. Given GF’s repertoire, it is perhaps no surprise that the brand’s first chronograph is unorthodox.

Examining the movement from the back side results in momentary confusion. But the confusion extends well beyond the moment. Many of the movement elements are clearly from a chronograph, yet the classical chronograph layout or construction is not discernible.

A large, open-worked bridge finished with thick frosting looks like a horizontal clutch arm at first glance. A number of steel levers and a column wheel are visible, but the construction doesn’t adhere to the classic chronograph architecture in any discernible way. The highly polished column wheel appears to sit somewhat isolated, while the visible steel levers seem to have familiar shapes yet undefined functions. 

Many traditional chronograph components, including the reset hammers and clutch, are not apparent. Much of the chronograph works look intentionally concealed, enhancing the mystery.

When the Nano Foudroyante EWT was launched last year, GF mentioned a special implement in the vertical clutch that reduces play during reset but didn’t disclose much about the exact specifications. 

By analysing patent European patent EP4451068A1 filed in 2023, the system becomes clear. There is a brake wheel 21 mounted co-axial with the vertical clutch assembly, which works in conjunction with a brake finger 27. The brake wheel is loosely kept in in contact with gear 5 by frictional elements on their sides. Gear 5 is powered by the going train (not shown). 

The patent’s authors argue that when the chronograph is reset, clutch elements induce play and even potentially reverse gear 5’s rotation slightly. Such an inversion, they argue, would backlash into the going train, affecting the supply of power to the escapement.

Extracted from EP4451068A1

The brake works as follows: for most of the time, finger 27 is not engaged with the fine teeth of wheel 21. When the wearer resets the chronograph, a toothed rack 29 attached to the resetting hammers makes pinion 30 turn. A cam 33 co-axial with the pinion guides follower 27a in its rotation. Following the cam profile (not unlike a rail), the finger 27 brakes wheel 21, then lets go when the reset is complete. 

The action practically ensures gear 5 is briefly secured during reset and not influenced by the rest of the clutch elements. Since wheels 21 and 5 are only kept together by light friction, gear 5 can still advance during reset, as it remains engaged with the going train. The brake only ensures any residual couple from the other clutch elements doesn’t interfere with gear 5. 

The solution, although elegant, seems too complex for what it promises to solve. Simpler chronograph clutches have been in use for some time now and not one addressed this of a specific issue. While GF’’s argument is reasonable, any sudden and very short-lived reversal of this kind of intermediary gear has in practice only an infinitesimal effect on the going train. 

Moving towards the outside, the arrangement of the pushers is unconventional. The button at two o’clock starts and stops the chronograph, while the pusher co-axial with the crown is for reset and flyback – very unlike traditional chronograph configuration.

The usual finish

Construction aside, the movement is classic GF style in terms of finishing.

All of the brand’s favourite decorative techniques are employed. There is exemplary black polishing for the steel levers and bridges, with light brushing on components buried deep. 

The usual rich granular frosting is applied the one-piece open-worked bridge that’s also finished with wide, rounded bevelling. Every jewel on the bridge sits in its own gold setting. 

There is an abundance of gears that are layered within the movement, making for an interesting sight. If it weren’t for the angular column wheel, there would be no hint that the calibre is a chronograph, but rather some unknown, exotic complication. 

A subtle reference to GF’s past work is the micro relief engraving on the chronograph seconds wheel, one of the handful of instances that GF has put this on a moving part instead of the case or bridge. The micro relief engraving is part of their established styling cues and something that adds sharp modernity to the otherwise classic-looking movement. Here “classic” refers strictly to the other finishing techniques, rather than the general appearance of the calibre. 

Even on the front, the impeccable finishing is evident on the simple hands that each boast a perfectly polished central hub. The axis of the seconds hand even features a countersink.

Concluding thoughts

Starting from CHF465,000, the Nano Foudroyante EWT is undoubtedly one of the more expensive watches on the market. Still under the almost CHF1 million-mark of the Hand Made line, the Nano Foudroyante EWT is a pricey and exclusive artisanal proof of concept, with only 11 watches to be made. The over engineering of the movement surely explains the limited run. 

Key facts and price 

Greubel Forsey Nano Foudroyante EWT

Diameter: 37.9 mm
Height: 10.49 mm
Material: White gold and tantalum
Crystal: Sapphire
Water resistance: 30 m

Movement: In-house flyback chronograph movement with one minute flying tourbillon
Functions: Hour, minutes,  small seconds, flyback chronograph, foudroyante, and flying tourbillon
Winding: Manual winding
Frequency: 21,600 beats per hours (3 Hz)
Power reserve: 24 hours with the chronograph running

Strap: Textile strap with white gold GF buckle

Limited edition: 11 pieces
Availability: From the Greubel Forsey and retailers
Price: CHF465,000 before tax

For more information, visit greubelforsey.com.

May 4, 2025: This is an expanded and refined version of an article first published in November 2024.