The acronym ‘GMT’, or Greenwich Mean Time, the benchmark meridian time, refers in watchmaking terminology to a (dual or) second time zone indicator. Driven by a spirit of research, Robert Greubel and Stephen Forsey have gone well beyond this conventional time zone display using a window or a hand, by incorporating into their timepiece a terrestrial globe completing each anti-clockwise rotation in 24h – the same direction in which our planet spins.
This planisphere presents all the global time zones in real time from the perspective of the North Pole where they converge. All the information can be viewed at a single glance. It is midday in the United Kingdom, and the beginning of the afternoon in Rome or Geneva. The eastern coast of the United States will soon be awakened by the early sunlight, while the Orient is still immersed in darkness… Our first contact with the timepiece offers an epic transcontinental journey. The GMT by Greubel Forsey is much more than a watch. It has evolved into a portable time map.
A lateral window set in the case offers a viewpoint over the Southern Hemisphere. The South Pole does not appear since it is the anchor point of the globe, which houses a “flying” pivot system. Greubel Forsey chose titanium, engraved with extreme precision in three dimensions to represent the continents in miniature.
The globe stands prominent at 8 o’clock, while the 24-second Tourbillon also protrudes at 5 o’clock. The platinum case has a third protrusion at 1 o’clock: the main time indications are clearly displayed, overlaid in a cascade across this area of the dial side , with a small seconds at 2 o’clock and then a sectorial power reserve indicator at 3 o’clock. At 10 o’clock is the GMT display for the second time zone.
The back of the timepiece displays universal time for 24 time zones, through an original rotating disc. This bears the names of 24 cities, and providing a particularly legible display, light-colored cartouches differentiating summer time (for cities which follow this system). As a final touch, a symbolic midday sun at the zenith of the world time disc illuminates the case- back, leaving centre stage of the dial side to the Earth.
Naturally, and in this too we can recognize the “Greubel Forsey signature”, the utmost care is taken with the decoration of the components, down to the smallest details. The hand finishes take in the entire range of traditional techniques, from frosting to hand-bevelling, as well as the subtleties of hand-polishing, lapping, and straight graining with flat black polished finishes. The domed crystal, the case-back and lateral window are made from sapphire crystal. The hand- stitched black alligator strap has a platinum folding clasp. A magnificent demonstration of expertise harnessed for the pursuit of fine craftsmanship.
The GMT calibre is powered by two barrels providing a 72-h power reserve with a frequency of 21,600 vibrations/hour. The calibre comprises 443 components. It features a 24-second tourbillon with 25° inclination, comprising 87 components for a total weight of 0.36 g.
Besides its chronometric properties and reliability, this regulator system was adopted for its small size, which meant that a calibre diameter of 36.40 mm (16 ½ lines) could be kept. This makes for a new medium-sized case, 43.5 mm wide with a total height of 16.14 mm. Made from 950 platinum, it has a slightly lighter hue than the previous white gold version.