Introducing The Greubel Forsey Nano-Foudroyante EWT, A Small Watch With Very Big Ideas

Greubel Forsey became famous after the brand’s launch in 2004 for several very good reasons, which include the extremely painstaking hand-finishing on its movements, the elaborate and almost microcosmic architecture of those movements, and perhaps most especially for the apparently inexhaustible inventiveness that its founders, Stephen Forsey and Robert Greubel, brought to the creation of complications. The company has created any number of highly complicated watches but its best known are its tourbillons which over the years have included multi-axis, double, and quadruple tourbillons as well as high speed tourbillons. In recent years GF has also experimented with less complex but no less well finished watches in the Balancier series, but lest anybody had gotten the impression that GF was no longer in the super-tourbillon business, they released, in 2023, the Tourbillon Cardan, which nestled an inclined tourbillon inside a double ring oscillating system. Today, GF has announced the latest of its EWT or “Experimental Watch Technology” inventions, in a limited edition series of 11 – it’s the Nano Foudroyante EWT, released to celebrate the brand’s 20th anniversary since its founding in 2004.

The nomenclature for Greubel Forsey inventions is a little confusing; the company is announcing this as its 10th fundamental invention although it announced an earlier version of the Nano Foudroyante in 2017 as its third EWT invention, distinct from its other “fundamental inventions” – the other two EWT inventions at the time were the the synthetic diamond Binomial escapement of 2009, and the Différentiel d’Egalité (a spherical differential remontoir, patented in 2006) which made it into a production watch in 2018; I don’t think the diamond Binomial escapement was ever actually produced. The original version of the Nano-Foudroyante was really more in the nature of a technology demonstrator, albeit as you would expect, an extremely impressive one.

A foudroyante, or lightning seconds hand (it is also sometimes called a diablotine, or “little devil”) is one that makes one full revolution per second, usually in distinct jumps that correspond to each unlocking of the escape wheel. Because the foudroyante is usually driven by a wheel mounted on the axis of the escape wheel, whatever gearing there is has to be as light and low inertia as possible so as to allow the escapement to lock and unlock correctly. (A more elaborate example of a foudroyante is F.P. Journe’s Centigraphe, in which there is the added complexity of engaging and disengaging the foudroyante hand when the chrono is switched on and off, as well as incorporating a reset mechanism and a way to brake the foudroyante hand in between jumps).

Diagram of the 2017 nano-foudroyante mechanism

The 2017 prototype introduced a new method, which was to use a micro-toothed wheel on the escape wheel axis, which was actually smaller in diameter than the escape wheel itself, by a considerable margin. This LIGA-fabricated wheel drives a crown wheel (again, extremely small) on the shaft of the foudroyante hand itself and since the rotation of this shaft was at right angles to the plane of rotation of the going train, the actual foudroyante hand and dial were built into the case band of the watch.

This time around, however, GF has gone for something more complex, but also far more practical and extremely ingenious.

The first thing you’ll notice, and be surprised by, if you are familiar with Greubel Forsey at all, is the size of the watch. Typically GF watches are quite large, partly for practical and partly for aesthetic reasons; a quadruple inclined tourbillon for instance is many things but it is probably not going to prompt anyone to write or say, “surprisingly wearable” (the Quadruple Tourbillon GMT, for instance, is 46.5mm x 17,45mm, albeit in addition to two double tourbillons, it also has a miniature globe of the Earth rotating inside it). The Nano Foudroyante, on the other hand, is just 37.9mm x 10.49mm in a white gold (case middle) and tantalum (bezel, caseback) case, which is smaller than some Grand Seiko time-and-date watches.

The second thing you’ll notice is the two pushers on the case flank at 2:00 and 3:00. The watch is a column wheel controlled flyback chronograph, with center chronograph seconds and a 60 minute counter at 9:00. The running seconds are visible at 8:30 on the dial. So far, so good, and also relatively conventional except for the slightly unusual subdial layout, and the use of a mixture of white gold and tantalum.

The main event however is the tourbillon, placed slightly asymmetrically and visible through an aperture between 4:00 and 7:00. This is a first for GF on a couple of counts. The first of the firsts, so to speak, is the fact that this is a flying tourbillon and for all that GF has created so many variations on the tourbillon, it’s never done a conventional flying tourbillon before (the closest it’s come is probably the Cardan, albeit what is technically the upper bridge is really part of the innermost gyrating ring). But what’s really going to catch your eye is the foudroyante dial which is sitting on top of the tourbillon itself.

The basic principle is the same as for the non-tourbillon 2017 version although obviously, the earlier model did not have the foudroyante hand and dial on the tourbillon itself. Since the escape wheel is on the tourbillon carriage (which is the case for all tourbillons) it is in principle just a matter of figuring out how to drive the foudroyante hand off the escape wheel, but – and it’s a big but – there is almost no room at all for the driving gears, unless you can shrink them down to a small enough scale to make the whole thing possible. There have been tourbillons with foudroyantes made before this but nobody has ever put one on the tourbillon itself. The foudroyante dial is a satellite – that is, it’s geared so that its vertical axis never changes; the 6 is always at the top of the dial no matter where the one minute flying tourbillon is in its orbit. Those of you with an interest in poising will notice that there is a very asymmetrical weight on the tourbillon carriage thanks to the foudroyante mechanism; GF has compensated for this with a platinum counterweight (hidden on the underside of the carriage).

The actual nano-scale drive system is in a housing under the foudroyante dial itself – I presume directly over the escape wheel – and the satellite gearing necessary to maintain the upright vertical axis of the system looks to be under the “GF” on the central axis of the tourbillon itself. The amount of energy used to drive the foudroyante is tiny – I’ll quote GF on this: “Compared to a traditional foudroyante that consumes 30μJ (microjoules) per jump, the Nano Foudroyante operates with only 16nJ (nanojoules) per jump, reducing energy consumption by a factor of 1,800. The mechanism’s volume is therefore reduced by 90%.” (The joule is an SI unit which corresponds, roughly, to the energy needed to raise a medium sized tomato one meter above the ground. You can use an apple if you’re a Newton fan). The 2017 system used a little bit less energy – GF told us 5 nanojoules per jump at the time – but that is still within an order of magnitude of 16nJ, and very reasonable given the adaptation of the drive system to a tourbillon.

If you want to be persnickity about terminology, “nanotechnology” generally refers to mechanisms which are on the one to 100 nanometer (billionth of a meter) scale, which is getting down into the size of individual atoms and molecules but I think we can excuse GF a little bit of hyperbole on this one. For comparison, 160 nanojoules is about the energy of a flying mosquito. This is fascinating watchmaking but it’s also fascinating engineering.

There is of course more to the story than the nanojoule engineering. For one thing, you would if you were interested in this watch (and by now I hope you are) and interested in GF in general you would hope that they hadn’t given up anything in movement finishing and this appears to be the case.

The movement is extremely compact; just 31mm in diameter (and if that number jumps out at you it is with good reason, this is the smallest movement GF has ever made). There is a single unified upper bridge for the movement (GF has not provided a caliber designation yet, but there’s certainly no reason to think you wouldn’t recognize this movement in an instant) and as far as I can tell, there is not a single inner angle that isn’t sharp as a sashimi knife, which is nice to see. GF has made a habit of inscribing text expressing its design philosophy on the dials and movements of some watches and here we have a little bit of the same thing, but as befits a 37mm watch from GF, on a demure scale and just on the center chronograph seconds wheel.

If you want to know how much energy any brand or watchmaker puts into finishing its movements two good places to look are the steady pins and screws; the steady pins visible on the movement are domed and black/mirror polished and the screws have beveled slots and heads and black polishing on every visible surface including the slots, slot bevels, and bottom of the slot itself. And, beveled countersinks, of course.

Greubel Forsey is one of the threee contemporary independent watch brands I wish I’d been able to collect from the beginning – the other two are MING and MB&F, all three somewhat for personal reasons (I say that but when it comes to watches all reasons I guess are personal). One of the most unforgettable moments I’ve ever had as a journalist and collector was sitting next to Stephen Forsey at a dinner in New York in the early oughts when the brand was launching in the US and hearing from him an hour long talk on the theory and practice of the tourbillon and the rationale for multi-axis tourbillons at the end of which I recall him saying, when I asked him if all this complexity really added up to any real chronometric advantage, that “It’s always a struggle to gain more than you lose.” It is quite wonderful to see GF still pushing the boundaries of mechanical horology, and astonishing to see them doing so in a 37.9mm watch; to put the Nano Foudroyante into a large case would have defeated the whole purpose of the exercise.

I hope to see one one day – at only 11 pieces, price on request, I don’t like my chances, but as a decades-long fan of watchmaking that doesn’t ask Why, but instead asks WHY NOT? I’m glad it exists at all.

The Greubel Forsey Nano Foudroyante EWT: case, 37.9mm x 10.49mm, white gold case with tantalum bezel and caseback; 30M water resistance. Gold dial, rhodium plated, engraved and black lacquered hour-ring and minute-circle opening for the tourbillon; small seconds and chronograph minutes counter in gold. Movement, nano foudroyante mounted on the one minute flyng tourbillon, monopusher flyback chronograph; hand wound running at 3Hz with 24 hour power reserve with the chronograph switched on. White gold pin buckle, hand-engraved GF logo; Price: CHF 465,000. Limited edition, 11 pieces world wide.