Sometimes, watch designers are free to come up with complicated mechanisms without troubling themselves too much about their efficiency. Chronometry – which means timekeeping precision – is often a secondary concern, even for watches equipped with tourbillons, exotic escapements and systems to reduce friction, which is a common obstacle to precision.
Arnold & Son designed the Constant Force Tourbillon precisely to make the most of two of these inventions – a tourbillon and a constant force mechanism – to produce a timepiece that ticks every box. The watch is elegant, technically forward-looking but traditionally inspired; its calibre A&S 5119 is perfectly symmetrical, finished with exceptional care and formidably precise.
Arnold & Son’s aim, supported by the La Joux-Perret manufacture to which it belongs, is to perpetuate the heritage of John Arnold, an English watchmaker who was active from the 1780s. Among his many contributions to the history of modern watchmaking, he appears to have coined the term “chronometer”. He designed marine chronometers that were very reliable, very precise and, because they could be mass-produced, affordable. In those days, the sea captain with the most accurate way of keeping time had a major strategic advantage, because he was able to calculate his position along the earth’s east-west axis, i.e. his longitude. John Arnold’s chronometers would have given His Majesty’s Royal Navy a considerable advantage.
Precision is the central concept behind the Constant Force Tourbillon. It uses a one-minute tourbillon that runs according to the usual principle, however, it is meticulously adjusted to ensure the greatest possible operating precision. The balance is non-annular and aerodynamic, and its high inertia protects it from shocks.
The tourbillon also benefits from a constant force mechanism. A system of intermediate springs, wound at close intervals, each store a small and constant amount of energy, which is delivered directly to the escapement. Because the energy is supplied consistently, the balance can beat in a uniform manner. The regularity and consistency of the force applied is an additional guarantee of precision. One side-effect of this system is that it allows for a dead seconds hand. Every time the spring is wound, the seconds hand jumps to the next graduation on the dial.
Together, the constant force mechanism and tourbillon of the Constant Force Tourbillon ensure that the watch achieves excellent timekeeping results. Privately, the company admits that this model achieves a precision of around 3 seconds per day on average. This is three times better than the chronometric standards on which the COSC bases its certification.
Nevertheless, the appeal of the Constant Force Tourbillon doesn’t stop at these arguments which, although crucial, have little relevance to what it’s like to wear. A watch lives on the wrist, and the appearance of the Constant Force Tourbillon has a great deal to recommend it. First, the design of the A&S 5119 calibre is a delight to connoisseurs of fine engineering. The two symmetrically arranged barrels in the upper half of the dial are counterbalanced by the tourbillon and constant force mechanism below. Almost all the visible bridges are skeletonised, and the hidden bridges are satin-brushed. The rear of the watch offers an almost identical view to the front. With its axial, central and lateral symmetry, the A&S 5119 is a study in balance and proportion.
Then there’s the case. This watch doesn’t really have a dial, unless you count the vestigial minute track punctuated with understated rose gold markers. Arnold & Son’s design makes the most of a sophisticated case profile with tiers and steps that add visual interest and make the watch broader where it touches the wrist than at the level of the bezel. The slenderness of the bezel ensures that the movement is given the greatest possible area in which to make its statement. Within the case diameter of 46 mm, 43 mm is left for the dial, making the Constant Force Tourbillon spectacularly panoramic.
