Zenith makes a marine chronometer for the wrist

In the theory of watchmaking, the tourbillon continues to divide specialists as to its usefulness in a wristwatch which, unlike pocket watches, is subject to a miscellany of positions. Rather than enter the fray, Manufacture Zenith has worked on the grounds that “the best position for an escapement is the horizontal position which ensures the best amplitude for the balance and on which gravity is perpendicular to the components and therefore does not disturb their rotation.”

Zenith goes on to remind us that a classic tourbillon inside a wristwatch enhances precision by correcting four positions out of six but is still lacking from this point of view. An inclined tourbillon, such as the ones by Greubel Forsey, or the Gyrotourbillon by Jaeger-LeCoultre (a spherical tourbillon with two cages set at a 90° angle and rotating at variable speeds) correct more positions, “but this is still the average of several errors, and they are only briefly in a horizontal position. The ultimate step thus lay in adapting the best solution, that of the constant horizontal escapement, to the wristwatch.”

An exceptionally complex mechanism

It took the Manufacture more than five years to reach this goal, inspired by the same principle which enables marine chronometers to maintain a horizontal position by mounting them on gimbals, a frame with two orthogonal pivot axes that supports an object which remains immobile irrespective of the movement of the frame. Taking this as their starting-point, Zenith’s design engineers imagined a gyroscopic system that maintains the regulating organ in a horizontal position. An additional difficulty was to apply this differential mechanism – a mechanical system that harnesses the speed of rotation and adapts it to suit this horizontal position – to a hand-wound movement beating at 36,000 vibrations/hour (5 Hz) with a 50-hour power reserve. Says Zenith: “The numbers give an idea of the sheer complexity of the task, since this daring complication comprises 166 components, while a tourbillon has approximately 66. The result is the first wristworn timepiece in which the rate is completely independent of its wearers’ movements.”

Zenith has named its timepiece in honour of the great navigator Christopher Columbus. “This ultra-complex model addresses one of the key issues that faced this adventurous seafarer and still haunts the contemporary watch industry to this day: how to achieve precision measurements with instruments that are subjected to constant motion that is detrimental to their accuracy.” Zenith has found its own solution.

The very principle of the Zenith Christophe Colomb has inspired a number of watch designers over the past decade. In 2004, Giulio Papi at Audemars Piguet Giulio Papi filed a patent for a “correction mechanism for the seating of a balance-spring regulator device” in the form of a regulating device whose escape wheel is kept in a horizontal position by a gyroscopic mechanism. A year later, as Business Montres reminds us, Laurent Besse followed suit with a patent to “counter the effects of the Earth’s gravitational force” with a reference plane and a balance mounted in a frame.

Zenith itself filed two separate patents. The first, filed in 2007, concerned “a correction mechanism for the seating of a balance-spring regulator device inspired by the double gimbals correction mechanisms used in marine chronometers to maintain a constant horizontal position.” The second, filed the following year, referred to the “need for a correction differential for each articulation axis” to be added to the previous patented mechanism.

Now it was “simply” a question of putting theory into practice, in particular with respect to transmission. The design engineers at Jaeger-LeCoultre had resolved the problem with a large centre wheel with inclined teeth to drive its inclined Gyrotourbillon, with a torque limitation device on the mainspring of the Gyrotourbillon II which stops the watch when there is no longer sufficient torque. As for the Zenith Christophe Colomb, energy is transmitted from the movement to the cage by three wheels outside the cage in the form of a dome. Three other parallel wheels and the reverser and differential intermediate wheels inside the cage neutralise its random movements. To minimise energy loss, all the synchronisation wheels are driven by the Earth’s gravity acting on the gold counterweight while each conical gear has been designed for maximum efficiency and specially made by Zenith on five-axes CNC machines.