The result of four years’ work, the Traditionnelle Twin Beat Perpetual Calendar (£195,000) can run for up to 65 days before needing rewinding. Its power reserve – the autonomy that movement has when fully wound – is a technical tour de force. If one thinks of it like miles per gallon, this is akin to driving from Moscow to Marbella on a single tank. Traditionally, power reserve has been extended by using a much bigger mainspring, or a number of mainsprings, which store more energy when fully wound, and by optimising the gear-train efficiency, so minimum energy is expended beyond that required to move the hands. Vacheron wanted to try something else, as style and heritage director Christian Selmoni explains. “The idea was to extend power reserve in a different way to adding barrels and barrels, so the Twin Beat has two gear trains. This is totally rethinking the question of power reserve in a mechanical watch.”
To return to the automotive analogy: as hybrid cars switch between petrol and electricity, so the Twin Beat wearer can select a high-frequency 5Hz oscillator or a much slower, less power-consuming one of 1.2Hz. The power comes from a mainspring housed in a double barrel at 12 o’clock. A differential system means that with the push of a button, the wearer can slip between normal and extended power reserve. This, combined with an instant jump system that accumulates energy throughout the day and uses four times less torque than normal to change the date, enables the extension to 65 days (though, Selmoni admits, the lower frequency performs best when the watch is lying flat). This achievement has focused attention on power reserve, an issue that currently occupies watchmakers as advances in technology permit significant gains.