Zenith Defy Zero G Sapphire and the Mechanics of Gravity-Defying Watchmaking

If the tourbillon is too basic for you, Zenith has the answer: the Zero G. While the tourbillon averages out rate errors by keeping the balance assembly in motion, the proprietary Zero G module keeps said assembly in the same position no matter how the wearer moves. When Zenith introduced this concept in 2008, it induced a lot of head-scratching and also plenty of concern about size. Today, the Defy Zero G Sapphire presents a Zero G module that occupies just 30 percent of the original’s volume. The original necessitated bulges on the sapphire crystal (creating a sort of bubble that appeared to house the module) and yet with the new Zero G Sapphire, no such measures are required.

This aside, though, the question of how keeping things in one constant position helps anything remains. There is a short (ish) answer but first, a few words are called for to describe the watch. At 46 millimetres, the Defy Zero G Sapphire is a commanding presence on the wrist (supplied specifications do not provide the height of the watch). The time subdial is in lapis lazuli, much like other anniversary pieces this year.

The Defy Zero G Sapphire is a time-only piece, with a power reserve indicator at 3 o’clock. Significantly, there are two versions, both in sapphire crystal (one clear, the other blue), adding a level of transparency to the watch — one can now see how the Zero G module does its thing. The astute amongst you will surmise that some kind of gimbal system must be in play, and that is right. Incredibly, Zenith has shrunk this mechanism to fit in just 1.3 cubic centimetres of space; it consists of 139 components, including a platinum counterweight and lubrication-free ceramic ball bearings (nine of them).

The movement designation here is El Primero 8812S, a rare example of an El Primero that is neither a chronograph nor an automatic. True to its legacy, though, it beats at a high frequency of 5 hertz or 36,000 vibrations per hour, ensuring precision to match its stability. The movement offers a 50-hour power reserve, indicated by the aforementioned display, while the small seconds are tucked away at 9 o’clock.

The complexity of transmitting power to a tumbling gyroscope cannot be overstated. Zenith’s engineers devised a system of conical bevel gears and a miniature differential to ensure that torque from the barrel is delivered consistently to the escapement, even as the module tilts and rotates in space. Again, it is worth recalling that the module is moving to keep the balance assembly still. The main benefit of being in one position regularly is that the movement needs only be optimised for accuracy in that one position. Even a normal balance in a pocket watch will find itself in more positions than a Zero G.

For more on the latest in luxury watch reads, click here.