Greubel Forsey reinterprets the Perpetual Calendar with Equation of Time

Greubel Forsey reinterprets the Perpetual Calendar with Equation of Time

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Greubel Forsey reinterprets the Perpetual Calendar with Equation of Time. To this effect, a mechanical computer had been created, which manages all the changes in the displays. The dial side mainly shows the 24 hours of the day and night, the day of the week, the large date, the month, the hours and the minutes; the movement side shows the equation of time and the seasons and the year.”

QP à Équation

Readability and displays
This reinvention of the perpetual calendar integrates the Equation of Time into the perpetual calendar, as well as bringing practical new functions and indications that improve clarity. The priority was to simplify a complete perpetual calendar display and yet make it much easier to set by simply using the bidirectional crown. Despite the numerous indications and functions, Greubel Forsey’s Mechanical Computer is as easy to set as a simple date feature.

To meet this technical challenge Greubel Forsey invented a sophisticated coding mechanism: the patented Mechanical Computer. A stack of cams with movable fingers shift the indications on the
dial and caseback of the timepiece and the complete mechanism is fully integrated within the movement. The month’s cam changes the month, displayed in a window on the front and also moves the Equation of Time disc on the back. The years’ cam controls the leap year indication on the front and also the millesime and seasons on the back. The development of this coding device not only overturns the conventional way of setting the indications but also displays them simultaneously on both dial and caseback.

Just a glance at the calendar display clearly reveals the three in-line windows that clearly indicate the day, the date and the month. The large date makes the calendar extremely legible.

QP à Équation

Two sides showing 15 indications

The dial side of the QP à Équation indicates leap years, the 24 hours of the day and night, the day of the week, the large date, the month, the hours, the minutes and the seconds, as well as the 72-hour chronometric power reserve.

On the movement side, this timepiece displays the Equation of Time with the months, seasons, solstices and equinoxes, as well as the calendar year.
The Equation of Time The Equation of Time merits further explanation. Horology seeks to measure time as regularly as possible; however the Earth orbits the Sun in an elliptical path. As the Earth sweeps close past the Sun, the period between successive solar zeniths, or the solar day’s length, changes. This causes the Two sides showing 15 indications difference  between solar time and mean time to vary from a few seconds to as much as 16 minutes during the year. The Equation of Time is the conversion factor between solar and mean time. To read solar time, simply look at the back subdial for the displayed date’s Equation of Time.

Greubel Forsey continues to put time to better service; where the caseback of the timepiece is not just there to showcase fine hand finishing, but also provides a new way to tell the time. The most frequently sought calendar information, namely the day, date and month, is displayed on the inline main dial display.  Information that is less often required is visible on the back of the timepiece. Thus the two sides show indications that you need to know regularly on the front, and indications accessed less frequently on the back.

Chronometry with ease
The timekeeping performance comes from Greubel Forsey’s third invention: the Tourbillon 24 Secondes, with its unique fast rotational speed and inclined angle to solve the problem of critical positions of the oscillator in relation to gravity. A 25° angle and the rapid revolution of the tourbillon cage significantly improve the chronometric performance of a system containing only one tourbillon, especially in stable positions. The multi-level chocolate-coloured gold dial of this millesime edition timepiece contrasts harmoniously with the 5N red gold case and underlines the intuitive linear calendar display. Herein lies the happy paradox:
it is an ultra-complicated timepiece with complete perpetual calendar, tourbillon and Equation of Time function, however, it is just as easy to use and adjustas a three hands watch. Thanks to the bi-directional correction, it can be easily adjusted in both directions without risk of damage to the movement.


QP à Équation
In 5N red gold – Millésimé
Chocolate-coloured dial
Hand-wound movement with 4 patents
Bidirectional perpetual calendar • day, date, month, calendar year, leap year, day/night •
equation of time with month, season, solstice and equinox • function selector •
Tourbillon 24 Secondes • hours and minutes • small seconds • power-reserve

QP à Équation

Movement dimensions
• Diameter : 36.40 mm
• Thickness : 9.60 mm
Number of parts
• Movement : 624 parts
• Tourbillon cage : 86 parts
• Weight of the cage : 0.37 g
Number of jewels
• 75
• Olived-domed jewels in gold chatons
Chronometric power reserve
• 72 hours
• 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
• Variable-inertia with gold mean-time screws
(10 mm diameter)
• 21’600 vibrations/hour
Balance spring
• Phillips terminal curve
• Geneva-style stud
Main plates
• Nickel silver, frosted and spotted with polished
bevelling and countersinks, straight-grained
flanks, nickel-palladium treatment
• Nickel silver, frosted and spotted, with polished
bevelling and countersinks, straight-grained
flanks, nickel-palladium treatment
• 4 engraved gold plates,
one with the individual number
• Flat black polished steel tourbillon bridges
• Synthetic sapphire mechanical computer bridge
• Inclined at a 25° angle, 24-seconds rotation
• Light alloy cage pillars
• Titanium cage bridges
• Gold counterweight
• Involute circle profile
• Tangential inclined gear on fixed wheel
and profiled teeth on escape wheel pinion
Dial displays
• Hours and minutes
• Small seconds
• 72-hours power reserve on a sector
• Day of the week, large date and month
• Leap year
• Day-and-night with red safety zone
• Function selection
(perpetual calendar or H/M time adjustment)
Back displays
• Equation of time with month,
season, solstice and equinox
• Calendar year
• In 5N red gold with asymmetrical convex
synthetic sapphire crystal
• Transparent back with asymmetrical synthetic
sapphire crystal
• Three-dimensional, variable geometry-shaped lugs
• Raised polished engraving “QP à Équation” and
“Greubel Forsey” on a hand-punched background
• Gold security screws
• Polished bezel, caseband with hand-finished
straight graining
• Hand-engraved individual number
Case dimensions
• Diameter : 43.50 mm
• Height : 16.00 mm
Water resistance of the case
• Water-resistant 3 atm – 30 m – 100 ft
(standard NIHS 92-20/SN ISO 22810:2010)
• In 5N red gold with engraved GF logo
• Multi-level gold dial, chocolate-coloured
• Gold hour markers
• Small second, power-reserve
• Leap year in polished steel, black treatment
• Gold perpetual calendar aperture with polished
raised engraving
• Gold GF logo
• Hours and minutes in polished gold
with Super-LumiNova
• Small seconds, power-reserve in polished gold
• Leap year in polished steel, black treatment
Strap and clasp
• Hand-sewn alligator
• 5N red gold folding clasp, hand-engraved
with the GF logo

(Pictures and information courtesy of Greubel Forsey)




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