The Greubel Forsey Double Balancier Convexe Has Two Hearts That Beat As One.
The Greubel Forsey Balancier S was introduced in August of 2020 and this year, the company is introducing a new version of the Balancier S curved case, fitted with double balance wheels, inclined at 30º.
The Double Balancier Convexe is, as is usually the case with Greubel Forsey, a large watch, at 43.50mm x 13.75mm (bezel diameter 46.50mm) but the titanium case, as well as its pronounced curvature, should make it much more wearable than you'd think from the hefty size. It's also water-resistant to 100 meters which means you could actually dive with it if you wanted to. The dial side of the watch is where most of the horological action is, and if you like borderline mad-scientist horological experimentation happily married to top-tier haute horlogerie finishing, you're going to love the Double Balancier Convexe.
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The basic idea behind an inclined balance is the same as the thinking behind the tourbillon – if the balance is not in the horizontal or vertical plane exactly, you tend to get less variation between positions because the balance is never in one extreme position or the other. Greubel Forsey has created inclined tourbillons as well, including the Quadruple Tourbillon GMT (which, like Potter's design, has the balances set at a 25º angle) but has also done interesting work with inclined balances. The ideal angle for canceling out rate variations would probably be 45º, however that would produce a very thick movement. You could get around this to some extent by using a smaller diameter balance but beyond a certain point this adversely affects precision, and so such watches are generally designed around a compromise value – in the case of the Double Balancier Convexe, 30º.
The idea behind using two balances is that even if one of the balances is in a completely flat or completely vertical position, the other will not be and the sum of their rates will be more precise than either one taken alone. The differential passes energy to both balances but since the hands of a watch are driven by the going train wheels, it also functions to average the rates of the two balances and produce a single rate which is displayed by the hands.
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Every surface is finished, and very elaborately finished – screws, for instance, have chamfered heads and slots, and are polished on top, on the flanks, on the chamfers, and in the slots (which is a lot of polishing operations for a single component). Generally, Greubel Forsey uses a combination of very traditional finishing techniques and more modern finishes, and the classic gleam of polished steel and brass is complemented in the Double Balancier Convexe with the anthracite color of the titanium mainplate. The Double Balancier Convexe is a limited edition of 66 pieces and price at launch is $328,000.