Greubel Forsey GF 05 GMT Platinum

In 2011, Independent Swiss watch brand Greubel Forsey revolutionized the field of GMT (dual time zone) watches with their innovative timepiece and its original technique, aesthetics and practicality. Its exceptional precision movement, featuring the 24-second tourbillon with 25° inclination, now comes set against a platinum backdrop.

Driven by a spirit of research, master watchmakers Robert Greubel and Stephen Forsey have gone well beyond the 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. A lateral window set in the case offers a viewpoint over the Southern Hemisphere. The SouthPole 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 caseback, leaving centre stage of the dial side to the Earth.

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.

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.

Technical details
Functions
2nd time zone GMT display
Tourbillon 24 Secondes
Titanium rotating globe with universal time display
24 time zone world time display
Summer time indicator
World time disc with summer time zones
Day-and-night indicator
Power-reserve indicator
Hour and minute display
Small second indicator
GMT pusher
Equatorial synthetic sapphire crystal lateral window

Movement
Calibre GF05
Mechanical hand-wound movement with patented tourbillon

Movement dimensions
• Diameter: 36.40 mm
• Thickness: 9.80 mm

Number of parts
• Complete movement: 443 parts
• Tourbillon cage: 87 parts
• Weight of the cage: 0.36 g

Number of jewels
• 50
• Olived-domed jewels in gold chatons

Power reserve
• 72 hours: Barrels
• Two coaxial series-coupled fast-rotating barrels (1 turn in 3.2 hours), one of which is equipped with a slipping spring to avoid excess tension

Balance wheel
• Free sprung variable-inertia balance with gold mean-time screws (10 mm diameter)
Frequency: 21’600 vibrations/hour

Balance spring
• Phillips terminal curve
• Geneva-style stud

Main plates
Nickel silver, frosted and spotted, hand-bevelled with countersinks, straight-grained flanks, black chrome treatment

Bridges
Nickel silver, frosted and spotted, hand-bevelled, straight-grained flanks, polished countersinks, black chrome treatment
Gold plate engraved with the individual number
Flat black polished steel tourbillon bridge, hand-bevelledTourbillon cage
Inclined at a 25° angle, 24-second rotation
Cage pillars in Avional
Titanium cage bridges
Gold counterweight

Gearing
Involute circle profile
Conical gearing with corrected profiles

Displays
Hour and minute
Small second
72-hour power reserve on a sector
2ndtime zone GMT indicator
24 time zone world time display
Rotating titanium globe with universal time display
Summer time indicator
Day-and-night indicator

Case
Platinum with asymmetrical convex synthetic sapphire crystal
Transparent back with asymmetrical convex synthetic sapphire crystal
Polished bezel and centre band with hand finished straight graining
Lateral window with shaped synthetic sapphire crystal
Three-dimensional, variable geometry shaped lugs
Platinum pusher with raised polished engraving “GMT” on a hand-punched background
Raised polished engraving “Greubel Forsey” on a hand-punched background
Hand-engraved individual number
Gold security screws
Case dimensions: Diameter: 43.50 mm & Thickness: 16.14 mm
Water-resistance: 3 atm – 30 m – 100 ft (standard NIHS 92-20/SN ISO 22810:2010)
Crown: In platinum with engraved and black lacquered GF logo

Dial
Principal hour-minute dial: in gold, frosted, black chrome treatment
Hour-ring: white gold
Gold power-reserve sector
Gold small second dial
Gold GMT indicator
Applied gold Greubel Forsey logo

Hands
Hour and minute in polished gold, with Super-LumiNova
Small second blued steel and power-reserve in polished gold
2nd time zone GMT indicator, red triangle

Strap and clasp
Hand-sewn blue or black alligator
Platinum folding clasp, hand-engraved with the Greubel Forsey logo

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