perpetual calendar is meant to show at least the hours, minutes, date, month and leap years up to 2100, theoretically without human intervention. Except that if it reaches the end of its power reserve and stops, you have to launch into a tedious re-setting operation. It’s a problem that Vacheron Constantin recently solved with a stroke of genius.

The solution? The name says it all: Twin Beat. The inspiration for it came from the Japanese clocks of the Edo period (1603 - 1868) in which day and night were divided into six segments of differing durations, which varied with the seasons. These clocks were equipped with simple or double foliot balances that enabled their speed of operation to be modified. So how could this kind of functionality be translated into a wristwatch?

Two distinct balance wheels

The Traditionnelle Twin Beat perpetual calendar is equipped with a double barrel and two mainsprings that transmit their energy to two distinct gear trains powering two equally distinct regulating organs functioning at two distinct frequencies. There is the “Active” mode, with a high-frequency oscillator at 5Hz (36,000 vibrations/h), offering a power reserve of four days; and the “Standby” mode, with a low-frequency oscillator vibrating at 1.2Hz (8,640 vibrations/h), offering a power reserve of at least 65 days!

With the aid of a simple push button at 8 o’clock, the user can switch from one mode to the other according to whether they are wearing it – at 5Hz the watch keeps perfect time regardless of any brusque movements by the wearer – or are leaving it rest in low-frequency mode. In that case, it only requires rewinding manually once every two months. Placed at the top of the dial, the power reserve is unique: depending on whether the chosen mode is Active or Standby, a single needle automatically displays 4 or 65 days.

THE VACHERON CONSTANTIN TRADITIONNELLE TWIN BEAT PERPETUAL CALENDAR has Geneva Hallmark certification and comes in a classic platinum case 42mm in diameter and 12.3mm thick, which contrasts with its highly contemporary-looking, dual-level skeleton dial decorated with a radial guilloché and sand-blasted finish.

The most pertinent of all perpetual calendars

When you transition from one mode to another, there is no lag in the time display and calendar indications, thanks to an instantaneous switching system that stops one oscillator at the exact instant that the other starts, an operation that takes a fraction of a second. At the heart of this highly innovative system is a differential that allows the hands to draw variable information from two gear trains for one reading of the time, whatever the selected mode. A second differential, mounted on the barrel, applies a suitable amount of torque to the Standby balance, the very fine and ultrasensitive hairspring of which (its section much finer than that of a human hair) was specially designed for this very slow beat. Lastly, two supplementary differentials provide the information specific to the single hand that indicates one of the two power reserves.

The 480 components of this calibre 3160 QP are contained in a space 6mm thick and 32mm in diameter. A real feat. CHF 210,000