The Heart of Precision

The search for precision has obsessed and fascinated engineers and scientists, who have carried the art of precision to ever greater heights, simplifying, studying, and adopting the most unusual formulas and materials in order to gain that tenth of a second per day, which at times has seemed an insurmountable obstacle. Just imagine: a chronometer with a daily error rate of 1 second has a relative error of less than 0,0000116!

These figures truly give one pause and force one’s respect for the people who daily seek to create a mechanism that is perfect according to the laws of nature, of physics, of chemistry, and which also takes into account requirements of metallurgy, practicability and esthetics. All this in order to create a formidably accurate instrument which can be worn on the wrist. Truly an art, beyond a shadow of a doubt. Indeed, when one looks beyond the technology, one always finds an excellent watchmaker, an artist whose skill and esthetic sense are able to reduce the marginal errors that even the most sophisticated machines are not able to eliminate.

Thus can be explained the tourbillon’s power to fascinate. This small, complex, and ceaselessly rotating mechanism resembles a tiny beating heart, whose infinite fragility and delicacy leaves one speechless with admiration. The tourbillon affords irrefutable proof that even in today’s electronic world, hand-made masterpieces will always be appreciated.

Flying tourbillon regulator by Alfred Helwig, made in 1927

The tourbillon is undoubtedly the most fascina-ting of all horological inventions. Evidence of this can be seen both in the results of auction houses and in the tendencies of today’s market. The best-selling watches in the high-end and luxury categories are those with tourbillon. Invented in 1795 by Abraham-Louis Breguet and patented in Paris in 1801, this mechanism was created in order to eliminate certain problems that seriously limit the accuracy of watches worn on the person. One of the main obstacles encountered by chronometer makers is the problem of position. Indeed, this high-precision instrument, whether it is a pocket chronometer or a modern-day wristwatch, never remains static, but is constantly subject to being moved.

Centrifugal error is caused when the balance spring dilates on the balance pivot during oscillation, when the instrument is laid flat. When it is in a vertical position, gravity “theoretically” cancels out positional error. This problem is caused by the constant expansion and contraction of the balance spring, even if it is isochronous, so that during oscillation, it exercises an irregular pressure on the jewel-mounted balance pivots, and consequently affects the precision of the instrument. Breguet’s idea was to reduce this error by making the escapement rotate, (in other words, the escapement wheel, the escapement and the regulatory organ, the balance ) thus resulting in a positional error which is constant. If the error is constant, it can be calculated, and thus regulated; if it is not constant, it cannot be regulated.

Put in colloquial terms, Breguet must have thought, “If the mountain cannot go to Mohammed, Mohammed must go to the mountain”. Whereas one cannot expect the wearer of a watch to keep it in constant movement, it is certainly possible to place a portion of the mechanism in constant movement. Translated into theoretical terms, the position of the watch matters little, if its regulatory organ (the escapement) is in constant and regular motion.

Breguet’s initial idea was to make a tourbillon with a rotation of a minute, because the indication of the seconds on the dial was mounted directly on the carriage pivot, which rotated once a minute. In the tourbillon system, the seconds wheel is fixed to the lower plate. The pinion of the escapement wheel on the carriage meshes with the fixed seconds wheel on the lower plate, and the rotation is transmitted to the carriage by means of an intermediate wheel which meshes with the carriage pinion. In summary, the intermediate wheel transmits the moving force of the mainspring to the carriage pinion, while the escape wheel pinion on the carriage receives the moving force from the carriage, and tempers it by turning around the fixed wheel.

There are several types of tourbillon regulators, some with a rotation of one-minute, some four-minute, some six, etc. Potter constructed one with a rotation of 5 seconds. Whatever the time of rotation, the tourbillon mechanism is an integral part of the motion train. By contrast, in the Karussel, an analogous system invented by Bonniksen 99 years after Breguet’s invention, the rotating plate (equivalent to the carriage in the tourbillon) is not an integral part of the motion train, but is driven by gears. It therefore transmits no force to any other wheel. In practical terms, the tourbillon system only functions if there is contact with the intermediate wheel, the Karussel system continues to function even if there is no transmission to the rotating plate.

A multitude of carriages of various shapes have been created by makers of tourbillons; some have two or three straight or equidistant arms, others have forms which are less geometrical and more elaborate, but are always placed so as to balance, by their position, the weight of the escapement. Certain of them have off-center escapements. Indeed, where as in a regular watch, the position of the escapement is not a determining factor in terms of precision, in the tourbillon it is vital that the balance between carriage and escapement be perfect. An error of inertia would transform a masterpiece of horological engineering into a mere gadget. Many famous watchmakers have made a contribution to the evolution of this mechanism; indeed, it has become a sort of idée fixe.