The ticking newcomer Audemars Piguet is presenting at SIHH 2016, namely the 3132 in the Royal Oak line, is something that watchmakers should by rights have stumbled upon before, given the growing number of mechanical voyeurs in the watch scene. One wants to see the beating heart of the watch. With tourbillons and models with peephole-perforated watch faces, this is now distinctly possible. In 2004, Frédérique Constant presented the house’s first manufacture calibre, the FC-910, with the balance wheel shifted to the front – just like that. So while it looked like a tourbillon, it was actually an entirely normal balance wheel oscillator.
“Millenary”, an Audemars Piguet model from 2011, offered a similar case. The family manufacture in Vallée de Joux took advantage of the ovoid case for the unconventional construction of the automatic calibre 4101. Despite a superficial similarity, this watch was as distant from a tourbillon as the Milky Way is from the Earth. For the sake of appearances the technicians reached for the trick of bringing the oscillation and escapement systems forward. And they put them in the prominent position to the left of the watch face, where the power regulator oscillates at four hertz. The constructive base for the 4101, made up of 253 components with 60 hours’ power reserve, was the round manufacture automatic 3120.
The watchmakers also used the proven platform 3120 for the skeletonised calibre 3132 in the “Royal Oak Double Balance Wheel Openworked”. Its unique feature, one that no-one had stumbled upon before, consists in the assembly of two balance wheels, together with their springs, on one balance staff.
One of the benefits of the “dual balance” concept – which of course has been patented – leaps out immediately. The oscillations of the front power regulator are unmistakable. It manages a full 21,600 oscillations every hour. The back balance wheel marks the imperturbable march of time with the same three-hertz frequency. Admittedly it only takes one of the two balance wheels to regulate. To change the moment of inertia there are a total of eight Masselots. The contrary actions of the pair of balance wheels can oscillate unimpeded by a regulating mechanism.
To reveal the other benefit of the double balance wheel system I have to delve into watchmaker theory. In the wearable mechanism of the watch, the relationship between weight and inertia must be optimally determined with a view to frequency and power reserve. As we know, the moment of inertia increases with the diameter. In any case, and this is something that mechanical watch enthusiasts should be aware of, the construction is such that the diameter can’t be increased at will.
The key factors in the decision process are frequency, power reserve and naturally the energy transferred to the oscillation system by the anchor wheel. For the stability of the movement, the achievable amplitude of the balance wheel oscillations and associated isochronism play an important part.
Georges-Albert Berner paraphrases the relevant law that applies to this in his illustrated dictionary of watchmaking: “For the watchmaker, the oscillations…of a balance wheel are isochronous when their duration is not dependent on the amplitude.” “The entire art of precise setting,” insists the one-time director of the Biel watchmaking school, consists in “achieving isochronism of the oscillations in the regulating units of the time-measuring instruments. The key factors that disturb the isochronism of the balance wheel springs, are the escapement, imbalance between the balance wheel and the spring, the play of the spring between the kerb pins, the centrifugal force, the magnetic field, etc.”
With wearable watches, it is often a good idea to have the balance wheel rotate at a high amplitude of 270 degrees, or more. The higher tempo makes the power regulator less sensitive to disruptive factors that can influence the duration of the oscillation. When vertical, the balance wheel amplitude is generally lower than in a horizontal position.
By deciding to include two concentric balance wheels affixed to one balance staff, Audemars Piguet increases the moment of inertia within the achievable diameter and with it, as was confirmed to me in Geneva, the stability of the movement.
But, and this is something that shouldn’t be dismissed out of hand, the greater mass influences the friction of the balance staff pins in the bearing jewels when the watch switches between vertical and horizontal positions. The watchmakers of Audemars Pigue have – as I was emphatically assured in Geneva – carefully considered all of these aspects in the development of the calibre 3132. They believe that the new double balance wheel system represents a good compromise between the various constructional determinants.
The so-called quality factor of the balance wheel suggests the quality of the oscillation system. It can easily be measured with a laser beam. When the anchor is removed, watchmakers move the balance wheel 330 degrees. This allows the electronics to measure how many oscillations balance wheel and springs can manage without additional energy reserves. For the well-known standard calibre Eta 2892-A2 this is around 300 in a horizontal position, but just 200 when held vertically.
By comparison, for the Breguet manual winding calibre 574 BR with magnetic pivots it is around 700 in both positions.
I approached Audemars Piguet for the value supplied by the double balance wheel calibre 3132 but they were unable to tell me. They are prepared to investigate, they said, and are aware that a new movement must come with cold, hard facts. “Our movement has an accuracy of between -2 and +8 seconds daily. With the double balance wheel calibre, this accuracy has been improved by 30 per cent.”
That two oscillating balance wheels require more energy due to the higher inertia can be see in the power reserve of the calibre 3132. After full winding it lasts 45 hours, whereas the 3120 base manages 60 hours. In contrast, the constructional height of the ticking microcosm has increased 1.3 millimetres to reach a total of 5.57 millimetres. Each of the movements, which are of course hand-skeletonised, requires 245 components. In the case and strap material of the Royal Oak there is a choice between steel, priced at 43,100 euros, and pink gold, at 75,100 euros.