The basic idea behind the tourbillon is to take the escapement and put it in a mechanically driven mount (or a group of nested mounts, in the case of the family of orbital tourbillons) in order to create a single average rate in all the vertical positions — and in many instances, to create a spectacular visual effect as well.
However, there’s another way to attack the problem. One of the criticisms levied at the tourbillon as a solution to the problem of rate variation in the vertical (or hanging) positions, is that it only creates an average of errors — it doesn’t do anything about the errors themselves. Even those fascinated by the tourbillon agree that for it to live up to its chronometric promise, it needs to be adjusted with great care.
While mass-production methods now mean that it’s possible to buy a tourbillon watch for less than US$2,000, a very well-made, well-adjusted tourbillon that gives excellent performance remains a rarity, and the greater complexity of tourbillons and multi-axis tourbillons mean, as Greubel Forsey’s Stephen Forsey once remarked to us, that “it’s always a struggle to gain more than you lose”.
Ingenious minds have considered the problem, however, and they have come up with a solution that is perhaps even more radical than the tourbillon. What if, the thought goes, you construct a watch in which there is no change in the position of the escapement, no matter what position the watch is in?
Like the tourbillon, it’s an idea with precedents. The basic solution is to put the timepiece in a gimballed mount so that no matter how it’s positioned, gravity always puts the watch or clock in the same position. Gimbal mounts are sometimes called Cardan suspension systems after Italian inventor Gerolamo Cardano (1501–1576), but the idea goes all the way back to ancient Greece: Philo of Byzantium, two centuries before Christ, described a gimbal system for holding an ink-pot upright. Such systems were then used extensively in marine navigation, first to hold compasses flat, and then for marine chronometers.
It’s the marine chronometer that inspired Zenith’s Christophe Colomb watch, probably one of the most delightfully distracting watches in the world. The Christophe Colomb is, in many respects, a very traditionally styled watch, replete with design cues designed to seduce with a promise of old-school chronometric excellence and high precision on which you wouldn’t hesitate to bet the fate of a ship at sea. The eye, however, is arrested by the large spherical enclosure formed by two domes — one in the upper crystal and one slightly smaller in the sapphire caseback — which contains a gimbal system in which the escapement beats at the fast pace of the El Primero family of movements (36,000vph).
Both the fast beat and the gimbal in which the escapement components and balance are mounted conspire to give the Christophe Colomb one of the most impressively stable rates we’ve ever seen in a watch. Zenith, with pardonable pride, has produced a video showing the results of positional tests of the watch on a professional timing machine, and the rate of the watch shows no variation at all.
The Christophe Colomb is a final refinement of the watch that was first introduced as a concept piece by Zenith in 2008 and which was originally called, perhaps regrettably, the Zero-G Tourbillon; the watch is emphatically not a tourbillon; and as a matter of fact, the way in which it is not is the whole point of the watch. (Misconceptions continue to stick to this watch, though. It’s been referred to as “gyroscopic” in some quarters and it’s no more a gyroscope than it is a tourbillon; the misunderstanding arises from the fact that gyroscopes in inertial navigation systems are mounted in Cardano/gimbal suspensions.) The most recent version of the Christophe Colomb ups the ante of exoticism even further and adds an additional touch of romance with the addition of an indication for the equation of time.
In the same spirit is a watch released last year by Cartier, and the product of what surely must be one of the most creative horological minds of our time: Carole Forestier-Kasapi (it is hard to avoid concluding that if you happen to find an unusual tourbillon nowadays, there are better than even odds that Carole had something to do with it). The Cartier Astrorégulateur is in the same lineage as the Christophe Colomb, in that it places the escapement on a mobile platform which is self-levelling, thanks to the fact that it swings freely on its mounting and is always under the influence of gravity. What makes the Astrorégulateur unique, however, is that the fourth wheel, escape wheel, escapement and balance wheel are all mounted on the micro-rotor that winds the automatic-winding system, which is located on the front of the movement and is visible through a large aperture in the dial, underneath a gorgeously black-polished steel bridge.
The bridge is reminiscent of the upper bridge that holds the cage of a classic tourbillon in place, but of course the Astrorégulateur is not a tourbillon, but a piece of horological trompe-l’œil artistry that provokes the same how’d-they-do-that wonderment as Cartier’s famous mystery clocks. Adding to the effect is the fact that the seconds hand is coordinated not with a seconds track on the dial, but rather with a seconds track on the swinging rotor — this is possible thanks to the fact that the fourth wheel in the going train is mounted on the mobile platform rather than on the fixed plate.
The question for the Christophe Colomb and the Astrorégulateur, is this: how do you get constant power across the discontinuity in the power flow created by the movement of the suspension system? The solution employed by each of these very unusual watches is to interpose a differential between the fixed mainplate and the moving escapement. The differential mechanically “subtracts” the motion of the suspension system — whether it’s a swinging winding mass or a Cardano-style gimbal mount — and ensures that an even power flow will keep the balance beating properly.
[Excerpted from an article by Jack Forster, first published in September 2011]