Anti-Gravity: Hands On With The Zenith Defy Zero G Sapphire
Zenith’s Zero G gravity control mechanism is an intricate alternative to the tourbillon.
Zenith is perhaps most famous for its high frequency, historically important El Primero chronograph movement, but behind the El Primero is a larger story of a continued search for higher precision in mechanical horology, which can be seen in both Zenith’s pioneering development of high beat calibers, and its many victories in the observatory chronometer competitions. In recent years, Zenith introduced a unique system for addressing the problem of variations in rate in positions with its Zero Gravity watches, which use a gimbal system adopted from those used to stabilize the positions of marine chronometers. The system can be seen in Zenith’s recently announced new Zero G watch, the Defy Zero G Sapphire.
The history of precision timekeeping is the history of gradual improvements to solutions in the same basic problems. These include isochronism, the effects of magnetism, the effects of temperature changes, and rate variations in different positions. Each of these problems has had different technical solutions over the years; the problem of variations in rate can be addressed through increasing the frequency of the balance and through improvements in techniques in adjusting to positions, but there are other possible solutions as well, including, most famously, the tourbillon. In marine chronometers, the problem of positional rate variation was partly addressed by placing the chronometer in a set of gimbals, which kept the chronometer in a dial up position regardless of the motion of the ship.
One of the first watchmakers to apply gimbals to the problem of making a marine chronometer was John Harrison, who placed his H1 sea clock inside gimbals mounted in a large wooden box. The origin of the invention is obscure; horologists prior to Harrison (including Christiaan Huygens) were aware of the potential value of gimbals in sea clocks, gimbals were used before the advent of marine chronometers – to keep compasses horizontal, for instance.
In pocket and wristwatches, the use of gimbals is almost but not completely unknown, although I know of just one example. In the year 1680 or thereabouts, the German watchmaker, Mattheus Hallaÿcher, made a watch which was regulated, not by a balance, but by a pendulum (with a verge escapement, Sotheby’s had it at auction in 2019.) The idea of a pendulum in a pocket watch seems prima facie absurd, but the first pendulum clock known had been patented only three years early (by Huygens) so from the perspective of the time, this was an attempt to incorporate what was then the last word in precision timekeeping into a portable device. Hallaÿcher was clearly aware that getting precision performance out of a portable timekeeper with a pendulum would be an uphill battle and so he bought himself, as he hoped, some insurance by putting the watch inside a double axis gimbal system.
Widespread adoption of gimbals doesn’t seem to have taken place, however, until the production of marine chronometers in large numbers began in the mid-19th century. In watches, a purely technical solution to the problem of varying rates in positions was largely addressed through careful adjustment, and careful poising of the balance; tourbillons remained rare and difficult to make, although they’re made in much larger numbers across many brands in the industry today. The use of gimbals in wristwatches on the other hand, is with the exception of Zenith, essentially nonexistent.
Zenith first debuted its Zero G Gravity Control “gyroscopic module” in 2008, in the Defy Xtreme Zero G. The Gravity Control gyroscopic module consisted of double gimbal system enclosing the escapement, balance, and balance spring, and energy reached the escapement and balance via differential gearing which transmitted torque across the gimbals even while they were in motion. The system was large enough in its first iteration to require a very thick case, as well as a sapphire crystal with a prominent bubble to enclose the gimbals, and Zenith would go on to pair the Gravity Control gimbals with a chain and fusée, in the Christoph Colomb series. (A Christoph Columb Zero G won the Complicated Watch Prize at the 2011 GPHG). In 2018, Zenith released a considerably smaller, second version of the gyroscopic module, which takes up just 30% of the volume of the original, and Zenith has recently announced the latest versions of the Defy Zero G in sapphire cases – blue, or completely clear, in limited editions of 10 pieces each.
The transparent sapphire model takes full advantage of the very dramatic reduction in size, and increase in general openness, of the new version of the gimbal system, which is now essentially suspended in space at 6:00 – the effect is fascinating and reminiscent of a mystery clock, in that it is far from immediately obvious how energy gets from the mainspring to the escapement and balance. The watch overall is still fairly large, at 46mm, but the reduction in size of the gimbal system means that it’s more wearable (and I would think, less accident prone) than earlier thicker models. The point at which the going train transmits energy to the differential gears surrounding the outer and inner gimbals can be seen from the back of the watch.
The wheel under the triangular bridge gears to a wheel on the outer gimbal, whose axis of rotation is along the vertical axis of the movement. The differential gears then pass the torque to the innermost gimbal, which is a hemispherical platform on which the balance, balance spring, and escapement are located. The underside of the inner gimbal, or platform, has a texture reminiscent of the cratered surface of the Moon.
The module’s purpose is essentially identical to the purpose of the tourbillon – that is to say, the elimination, or at least reduction of, variations in rate between positions. The tourbillon approaches the problem by rotating the escapement, balance, and balance spring through all the vertical positions to obtain a single average rate, which is then adjusted to match the rates in the vertical positions; modern multi-axis tourbillons, produced by companies such as Greubel Forsey and Jaeger-LeCoultre, attempt to adapt the tourbillon to the wristwatch by adding an additional axis of rotation.
The Gravity Control gimbal system, on the other hand, approaches the problem by placing the regulating organs in a gimbal system which keeps the regulating organs from ever departing from the horizontal position – normally a watch must be adjusted in dial up and dial down positions, but the Gravity Control system keeps the regulating organs in a single position at all times, which means the watch should never vary on its rate. How well the system works, depends on how good a job it does at making sure the regulating organs remain in the flat position.
The transparent case gives the watch a spectral presence which is accentuated by the lapis lazuli dial (blue is a signature color for Zenith, along with the star, which together represent the night sky). The lapis lazuli chosen for the dial has minute inclusions of gold-colored pyrite, which add to the night sky effect, and from a design standpoint alone, this is a very well thought out watch. The bridgework is part of the design as well, and not just for its transparency; it’s in the shape of Zenith’s emblematic five pointed star.
While the very first Zero G watch had a deliberately futuristic design, subsequent versions have adopted a more classical approach, and while the Zero G Sapphire is not quite as overtly reminiscent of the marine chronometer heritage as the Christoph Columb models, it still manages, despite the use of modern materials like synthetic sapphire for the case, to feel classical in execution (although with, perhaps, some elements of classical Modernist design as well).
The movement is Zeniths El Primero caliber 8812, which runs at 5Hz/36,000 vph, with a fifty hour power reserve.
The star of the show, if I can make a feeble pun, is of course the “gyroscopic module” (the name raises the question of whether there is actually a gyroscopic effect, about which more in a minute). As we’ve seen, the system rotates along two axes – the outer gimbal rotates on the vertical axis of the movement and the inner, on the horizontal. The balance spring is flat, with a regulator for fine rate adjustment, and in a nod to Zenith’s record setting chronometer movement, the caliber 135, Zenith has used that movement’s famous “fork tailed” regulator sweep, which was originally developed to make fine rate adjustments easier. You can also see, through the gap between the twin tails, the iridescent blue gleam of the silicon escape wheel (the lever is a combination of silicon and nickel; I assume the lever itself is nickel, with silicon pallets). The entire system uses 139 components, in a space of about 1.3 cubic centimeters (13.40 mm x 10.90 mm x 8.84 mm).
The gyroscopic module is related to the tourbillon in terms of the problem it was designed to address, but it’s similar in another respect as well, which is that the additional gears introduce additional friction and therefore have the potential to steal energy from the escapement and balance, in the same way that the extra mass of the tourbillon carriage requires more energy from the going train than if the escapement and balance were not enclosed in it. This means that very high precision machining is necessary, as well as close attention to reducing friction wherever possible (this includes the use of ceramic ball bearings in the gimbal system).
The Zero G watches raise several interesting questions whenever Zenith releases one. The first is how well the system actually does its job. The potential gotcha with the gyroscopic module is that it’s much smaller and lighter than a marine chronometer in its gimbals, and the movements to which it’s exposed are much more rapid and higher in amplitude relative to its size, than the oscillating motions of a ship at sea on the waves. And indeed, with the watch not running, the gyroscopic system oscillates briskly when the watch changes position. The second issue with how well the gyroscopic module works has to do with the fact that it is a double axis, not a triple axis system.
Let’s take the second question first. The module is free to rotate around the vertical axis of the movement; let’s call that the Y axis. It is also free to rotate around the horizontal axis; let’s call that the X axis. It is, however, not free to rotate around an axis – call it the Z axis – co-axial with the balance, which means that theoretically, it might be possible to put the balance in a non-horizontal position, if you rotate the watch around the Z axis.
And it is indeed possible. In the above image, the watch is in the crown right vertical position, and inclined to the left about 35º-40º. As you can see, the balance is slightly off the horizontal position, so the absence of the ability to rotate around our Z axis does mean that the system does not perfectly account for changes in position; in the terminology of mechanics, we would say that the gyroscopic module has two degrees of freedom rather than three. (In gimbals used to mount gyroscopes for inertial navigation systems, three gimbals and three degrees of freedom are necessary).
However, this is almost entirely a theoretical rather than a practical problem. This position is inherently unstable (it took repeated tries to get the gimbals in the positions seen above) and it takes almost no disturbance at all for the gimbals to rotate into a stable position. In fact, the gyroscopic module stayed in this position for only a few seconds and then, with no visible external disturbance at all, rotated into a new position with the balance horizontal again.
In actual use, I would say the odds of the gyroscopic module ever being in anything other than a flat position long enough to produce a detectable positional rate variation are slim to none. Marine chronometer cases, by the way, typically used a double gimbal system as well; there was no need for three degrees of freedom in those instances either. The only time you might want a marine chronometer to be able to rotate around its Z axis would be in a situation where the ship has rolled 90º at which point, if you are on board, you probably have other more urgent problems.
Moreover, if it were possible for the gimbal system to rotate in a direction co-axial with the balance, this would increase the risk of disturbing rate stability, as any such rotational motion would be transferred directly to the rotation of the balance.
Another question is whether or not motion induced oscillations, in which the gyroscopic module swings around its axes like a pendulum, might upset the balance on its rate. As we’ve said, at first glance, the module does indeed oscillate rather briskly if the watch is handled. However, I was curious whether or not it would do so if the watch was actually running. With some energy wound into the mainspring, the oscillations were damped considerably. The module went frrom swinging so rapidly when moved that it was difficult to count the oscillations, to oscillating at much lower amplitudes when the watch was running, and for only a couple of oscillations at most. I’m not sure why this happened but one possibility is that the torque passing through the differentials puts just enough load on the gears to dampen excessive oscillations of the module.
Finally, and on a related note, the question has arisen periodically since the module was introduced in 2008, as to whether it is actually gyroscopic, which is to say, whether or not the motion of the balance can cause a gyroscopic effect which might contribute to stabilizing the module. The question comes up partly because the mass of the balance is very low, and partly because in a gyroscope, rotation is in one direction only, while a balance swings alternately in two directions. I was not on Team Gyroscopic at first but as it turns out, surprisingly enough, the oscillations of the balance do allow it to act as a gyroscope.
A gyroscope’s position tends to be stable thanks to the principle of conservation of angular momentum, which states that a rotating object will tend to resist changes in its axis of rotation from external forces, proportional to its mass, radius of rotation, and speed of rotation. A balance is capable of holding a stable rate partly thanks to conservation of angular momentum and the amount of angular momentum produced by a balance is, and this is pretty wild, big enough to actually cause the case of a watch to rotate in the opposite direction of the balance. We know this because some folks at a lab at UC Santa Barbara actually mounted a watch in a vice that allowed it to rotate around its horizontal axis and then fired a laser at it – the case rotated back and forth enough to leave a visible horizontal trace from the laser when it was reflected off the case onto a target. The gyroscopic module would therefore seem to be actually gyroscopic, impossible though it might seem at first, and this may contribute to stabilizing the position of the module as well.
I came away from the whole experience very much impressed with both the Zero G gyroscopic module, and with the watch as a whole. Far from being what you might call a gimmick – and an expensive one to boot – the gyroscopic module appears to have been very carefully engineered and refined over the years to offer what seems to be a very plausible technical alternative to the problem of variations in rate in positions. I was particularly struck by the difference in the behavior of the module with the watch in an unpowered versus a running state, which seems to suggest that the team who designed it, designed it specifically for optimized dynamics when the watch is running. And I think this is overall the most successful version of the Zero G concept thus far – the aesthetics are extremely compelling and it says something about how far we’ve come since 2008, that the mechanics and the overall design support rather than compete with each other. A very limited release of a very unusual mechanism, but one with enormous interest for anyone intrigued by the pursuit of precision, and interested in whether or not innovation in watchmaking is possible.
The Zenith Defy Zero G Sapphire, ref. 04.9003.8812/51.R584: case, full transparent sapphire, 46mm, openworked skeletonized movement with lapis lazuili dial. Hands and indexes, rhodium plated, with Super-LumiNova SLN C1. Water resistance 30M. Movement, Zenith El Primero caliber 8812, running at 36,000 vph/5Hz, with Gravity Control gyroscopic module; 50 hour power reserve. Limited edition of 10 pieces in transparent sapphire, and 10 pieces in blue sapphire; price at launch, $207,500. The 1916 Company is proud to be an authorized retailer for Zenith watches; contact us for availability.