Greubel and Forsey have built a name for themselves creating high-end watch complications including four different tourbillon-based watches, such as the formidable “Quadruple Tourbillon à Différentiel” (QDT).
For their latest mechanical marvel the Greubel Forsey GMT they have turned their attention to creating a timepiece that displays a universal world time and a second time zone in a highly legible way. Lets explore its technical features.
The three dimensional titanium globe is fixed in one place: the south pole so it has greater freedom to rotate and it turns a full revolution in 24 hours anti-clockwise – the Earth’s natural rotational direction viewed from North pole.
Using the 24 hour day-night indicator via the equatorial chapter ring you can determine the position of the continents and the night-time hemisphere – 18:00 to 6:00 – is indicated by a blackened half of the ring around the globe, while the daytime hemisphere – 6:00 to 18:00 – is indicated by a whitened portion. The latter is superbly enhanced by a lateral window cleverly integrated into the case-band that lets in light to symbolize daytime.
Complimenting the globe is a second time zone dial at the 10 O’clock position giving the precise time in a second country of your choice and adjusted easily using the “quick-set” button top-left.
Radiating down from the top right are three main time-telling dials; the hour / minute dial at the top, below it a smaller seconds dial, and still smaller beneath that the power reserve can be read.
At the bottom is one of Greubel Forsey’s major patented inventions: the 25° inclined Tourbillon 24 Secondes cage. It was chosen not only for its superb chronometric virtues and reliability abut also its compact size which allows space for other complications.
This side of the Greubel Forsey GMT is barely less impressive and features a beautifully crafted ‘worldtime’ disc bearing the names of 24 cities each representing one of the different global time zones. Aligning the relevant city with the local hour on the outer chapter ring – or inner ring for cities with summer time – sets the dial-side globe in the correct position.
A gleaming sun completes the display back and provides a visual reference for midday on the worldtime disc .
Greubel Forsey GMT Technical Specifications
The movement consists of 436 components, 87 of which are used in the tourbillon cage, which weighs in at just 0.36 grams. Two coaxial mainspring barrels connected in series provide a power reserve of 72 hours and the movement is equipped with a variable inertia balance beating at 21,600vph/3Hz and a Phillips terminal curve balance spring.
Plates and bridges are hand-finished, frosted, spotted, bevelled, straight-grained, matt lapped and flat black polished. The dial is in 18k gold and the whole movement is housed in a white gold case of 43.50mm in diameter with a height of 16.14mm. The case is completed by domed sapphire crystals for the dial-side, display-back and lateral window, all treated with anti-reflective coating. The timepiece is complemented by a hand-sewn black alligator leather strap with a Greubel Forsey folding clasp in white gold.
Details on pricing and availability haven’t been released yet.