Double Tourbillon 30°

Two carriages, at different speeds, one of them inclined

Watch it run. The inner carriage rotates quickly and is visibly tilted out of the dial plane; the outer carriage rotates slowly and carries the whole assembly with it. Two nested rotations at different rates, in different planes, is a mechanism — not an appearance — and a few seconds of observation distinguishes it from a decorative aperture or a single conventional tourbillon.

Finishing quality is the specification and fails distinctively when imitated

At this level the finishing is the product. The diagnostic is geometric rather than aesthetic: a rotating tool cannot reach into a sharp internal angle, so machine bevels round off at internal corners and hold a uniform width, while hand-applied bevels reach a crisp point and vary slightly along their length. Black polish — a flat surface reflecting either pure black or pure white depending on angle — is likewise a hand process with no machine equivalent. Examine the internal angles of the bridges and the tourbillon cage.

At a hundred watches a year, ask the manufacturer

Greubel Forsey's total annual output is smaller than a single reference's run at most brands in this catalog. The manufacturer knows every watch, and confirmation of a serial and its service history is obtainable and decisive. A watch at this price that its maker will not confirm is a serious finding.