Staying Power: Vacheron Constantin Traditionnelle Twin Beat Perpetual Calendar

You can admit it: how many times have you read about an amazing perpetual calendar watch (we’ve written about quite a few) that touted as a top attribute the fact that it would remain accurate and not need resetting until some year far in the future, most likely after you, the prospective owner, have exited this mortal coil? And how many times have you rolled your eyes at such a boast, realizing how very unlikely, nigh impossible, it would be that any watch would remain in constant use, never unworn, never idle, never in need of a re-wind or re-set, for many decades at a time? Well, Vacheron Constantin unveiled a watch at SIHH 2019 today that makes such a scenario just a little more plausible. The new Traditionnelle Twin Beat Perpetual Calendar claims as its highest technical accolade its ability to function closer to “in perpetuity” than any perpetual calendar that preceded it.

The Vacheron Constantin Traditionnelle Twin Beat Perpetual Calendar, with its innovative and patent-pending mechanism, allows its user to switch the frequency of its movement from active mode, in which it beats at a speedy 36,000 vph (5 Hz), to standby mode, in which it drastically slows to an energy-conserving 8,640 vph (1.2 Hz). The answer to the horological puzzle that Vacheron’s watchmakers took on in their development of the new movement, Caliber 3610 — the assumed fixed timespan of a watch’s power reserve based on its mainspring barrel’s output — was the use of two separate balances, each operating at a different frequency, with a “mode selector” to switch from one to the other. Only one balance can oscillate at a time, so the watch’s wearer can switch the output based on his activity: most likely keep it in Active (36,000 vph) mode while wearing it for day-to-day activities and switch it to Standby (8,640 vph) to before taking it off for extended periods. In Active mode, the watch’s power reserve is four days; in Standby, this can be stretched to at least 65 days, meaning that even if the watch is kept in a safe or a drawer for two months, all its calendar functions will be up to date and accurate when the owner straps it back on.

Additionally, the “Twin Beat” system — whose mode selector, controlled by the pusher at 8 o’clock, ensures that only one balance oscillates at a time — is constructed so there is no lag in transitioning from one mode to another and no interruption in the timekeeping, even for a fraction of a second. Both balances are driven by one mainspring barrel, which is the most efficient way to distribute energy and allows the use of a single power-reserve indicator (with two scales, positioned on the dial side at 12 o’clock). Of course, the system required the creation of an entirely new, highly sensitive hairspring for the standby balance — one nearly four times smaller in cross-section and substantially more delicate than the more traditional hairspring used in the Active balance, comparable to a fine human hair. Caliber 3610 QP is also equipped with two balance wheels, only one of which operates at a time depending on the mode, with a gear differential that allows the hour and minute hands to draw information from both wheels for an accurate display of the time (yes, even the most basic aspects of timekeeping required some micro-mechanical derring-do in this watch).

In addition to the dual power-reserve indicator, the openworked dial hosts the mode indicator at 9 o’clock and two subdials for the date and day in the lower portion, with the leap year status sandwiched between them on another smaller subdial. Its engine-turned, frosted surfaces boast radial guillochage and sand-blasted finishes and white gold hour indices and hands. The reverse side of the manually wound movement also features high-level decoration, with plates and bridges graced with côtes de Genève and treated with a dark NAC coating that also aids in durability. And all of this groundbreaking technology has been accomplished in a smaller package than one would probably imagine. The case, made of 950 platinum, measures just 42 mm in diameter and 12.3 mm thick, housing a movement that is made up of 480 components yet comes in at fairly modest dimensions of 32 mm diameter and 6 mm thick. The whole ensemble is mounted on a gray Mississippi alligator strap that matches the slate-colored tones on the dial and closes with a platinum Maltese cross-shaped pin buckle. And fans of the Vacheron Constantin brand can be assured that the timepiece meets all the strict technical and aesthetic standards to earn it the prestigious Hallmark of Geneva. The Traditionnelle Twin Beat Perpetual Calendar (price on request) will be sold exclusively in Vacheron Constantin boutiques.