Even though watchmaking has grown more complex over the centuries, it has nevertheless always remained attached to the same objectives, and to the same obstacles standing in its way. Among these objectives, the foremost—by far—is the quest for precision.
Currently, a low-level Asian movement can display deviations of +/- 10 seconds per day, or even (much) more. A Swiss Made movement is about half that. A chronometer-certified movement ranges from -4 to +6 seconds per day. Other private certifications (Breguet, Omega, Rolex, among others) go even twice as low. That gives a sense of the orders of magnitude.
As for the obstacles that alter chronometry, they have been known since the dawn of watchmaking: shocks, accelerations, variations in temperature and humidity, and, more recently, surrounding magnetic fields. These exogenous factors may seem very heterogeneous. In reality, they are not: they are united by the fact that they all exert their deleterious effects on a single, unique component—the escapement. One should not conclude that a perfect escapement will solve all problems at once… but it comes close! And that is precisely what Zenith’s Zero G aims to achieve.
Why “Zero G”?
The G is an acceleration factor. This may be surprising, because the “g” it refers to (written in lowercase in scientific literature) does not measure acceleration itself, but rather Earth’s gravity. What is the connection between gravity and acceleration? Simple: gravity affects all terrestrial bodies through the acceleration it induces to bring that body to the surface — the famous Newton’s apple! The lighter object (the apple) is attracted by the heavier one (the Earth) at a speed proportional to its mass (the apple falls faster than the leaf from the tree). It is thus clear that gravity, g, is an acceleration factor that affects all objects on Earth… including a watch’s escapement. Admittedly, it is very light, but its mass is not zero. The escapement is therefore also drawn toward the center of the Earth, like any other physical body, and its components, such as the balance spring, can be slightly deformed. This, ultimately, will affect the watch’s precision. Hence the importance in watchmaking of designing an escapement that is as insensitive as possible to gravity g. Or even completely insensitive: the famous Zero G.
Maximum simplicity
The Zenith Zero G escapement has often been given definitions that are not its own: tourbillon, gyrotourbillon, etc. It is none of these. It is much simpler: it is an escapement mounted on a gimbal, that is, a mobile cradle whose balance of masses ensures it always returns to the horizontal. To simplify further: the Zero G is an escapement that is always horizontal, parallel to the ground. End of story… but one question remains: why is it interesting to have an escapement always parallel to the ground, in terms of chronometry?
The answer is simple: because all its components are certainly still affected by gravity, but in a uniform, homogeneous way. The g will affect all the elements of the escapement with the same force. The balance spring will therefore not be more deformed than the balance wheel, for example. In the end, the escapement functions as if there were no gravity. Of course, gravity still exists (which is why the term “Zero G” can be misleading), but technically speaking, almost all of its effects are eliminated.
A large family
The Zero G concept is more than 15 years old. Zenith has kept it alive through several models, and the escapement itself has evolved. Its size, in particular: in 2018, Zenith reduced it by 70%! That is colossal: the current Zero G now occupies only 30% of its original volume. Today, it fits into just 1.3 cm³.
There have also been several artistic versions (the Christophe Colomb series, SIAR, Cohiba cigars), as well as a few limited editions (Rolling Stones) and associated minor complications, including the small seconds and power reserve. In terms of materials, the balance spring and escape wheel have been made of silicon for about ten years, and the pallet fork of nickel-silicon. Zero G is the name of the model; the escapement itself is a module, which is called Gravity Control.
Two new limited editions
In 2021, Zenith reinterpreted this high-end watch caliber, redesigning its architecture for a more open and spectacular display, all housed in a transparent sapphire case that reveals the movement from every angle. To celebrate its 160th anniversary, the manufacture presents two new limited editions of the DEFY Zero G, in 46 mm cases of blue or transparent sapphire. The case middle, bezel, and back are cut from blocks of sapphire, a material almost as hard and scratch-resistant as diamond.
Continuing this anniversary theme, the off-centered hours, minutes, and seconds are read on a lapis lazuli dial, punctuated with faceted luminescent indices. Its deep blue, sprinkled with golden pyrite inclusions, evokes a starry sky, giving each piece a unique character. The 50-hour power reserve is displayed at 3 o’clock.
And tomorrow?
The Zero G concept still has a bright future ahead. First, in terms of complications. It is “only” an escapement, so one could imagine it paired with a chronograph, a date, a moonphase, a day-date, a GMT, and many others. In terms of materials, the possibilities for finishing are almost limitless (titanium case, carbon, etc.). Considering that Zenith and TAG Heuer belong to the same group, the new carbon balance spring from the latter could be incorporated into the Gravity Control of the former. Conversely, why not imagine a Zero G signed… TAG Heuer? Or even Hublot, the third brand in the LVMH group?
