The beauty of the Retrograde Annual Calendar lies in the fact that wearers need to adjust their watch only once a year. While the date automatically adapts to the respective length of 30- and 31-day months, it counts 29 days for the month of February whatever the year. This means that once a year – or rather three out of every four years – at the end of February, the wearer of the TONDA Annual Calendar
must slip the watch off their wrist and reconnect with its subtle mechanism by setting the date manually. It will then keep faultless track of the date for the next 365 days. The retrograde date indication never hinders the reading of the moon phases at 6 o'clock, placing this lyrical complication in the spotlight. To ensure perfect clarity, the day of the week and the month are indicated in separate apertures at 9 and 3 o'clock respectively.
THE PRECISION MOON PHASE:
The moon phase of the TONDA Annual Calendar complements the date indications. It is called a "precision moon" because it requires only one correction every 122 years. This remarkable accuracy involves compensating for the discrepancy between a classic lunar cycle (29 days and 12 hours) and the real lunar cycle (29 days, 12 hours, 44 minutes and 2.8 seconds). The TONDA Annual Calendar displays two depictions of the Moon – viewed from the Earth’s Northern and Southern hemispheres – so as to match any wearer's geographical location. The moon subdial and moon lozenges in solid rose gold stand out against an aventurine glass sky that poetically evokes the twinkling of a star-filled galaxy.
THE GREGORIAN CALENDAR, SUCCESSOR TO THE JULIAN CALENDAR:
Until 1582, Christendom used the Julian calendar instituted by Julius Caesar and based on the assumption that the length of the tropical year (the time between two transits of the Sun at the vernal point) is exactly 365.25 days. However, the actual length of the year is 365.24219 days, so that the recurrent events represented the equinoxes and solstices were moved forward by one day every 128 years: around the year 1500 CE, the spring equinox occurred ten days earlier than in ancient times, on 11 March instead of 21 March. In addition, the calculation of the date of Easter, which involves the Moon,
had become completely wrong. The Council of Trent therefore commissioned Pope Gregory XIII to redress the situation. With the help of scholars Christopher Clavius and Aloisius Lilius, he first removed ten days, so that the day after Thursday 4 October 1582 would be Friday 15 October. He then decided to eliminate three leap years in four centuries: only the century years divisible by 400 would remain leap years: this meant that 1700, 1800 and 1900 were not leap years, whereas 2000 was. This solution proved satisfactory and the Gregorian calendar, while not immediately adopted by all countries, is now used around the world, although some religions and societies retain their own calendar for ritual reasons.
Functions
Hours, minutes, seconds, retrograde annual calendar and precision moon phase
Hands
Hours and minutes: 18ct gold rhodium-plated skeletonized delta-shaped
Calendar and seconds: Rhodium-plated steel
Bracelet
Polished and satin-finished platinum 950
Closure: 18ct white gold folding clasp
Movement Specifications
PF339 – AUTOMATIC WINDING MANUFACTURE MOVEMENT
WITH RETROGRADE ANNUAL CALENDAR AND PRECISION MOON PHASE
Power reserve: 50 hours
Frequency: 28,800 Vph (4 Hz)
Jewels: 32
No. of components: 359
Total diameter: 30.6 mm
Thickness: 5.5 mm
Decoration: Côtes de Genève, beveled edges, Perlage
Oscillating weight: Platinum, skeletonized, polished and sandblasted
Dial Specifications
Material: Platinum 950
Finishing: Sandblasted
Indices: Hand-applied 18ct gold rhodium-plated appliques
Moon phase: Blue aventurine
Platinum
PFK999-2020001-200182
Case Specifications
Polished and satin-finished platinum 950 with knurled bezel
Diameter: 42 mm
Thickness: 11.1 mm
Crown: Ø 6 mm, screwed-in
Glass: ARunic anti-reflective sapphire Case back: sapphire glass
Engraving on case back: Serial number – “PARMIGIANI FLEURIER” – “Edition Limitée de 3 pièces”
Water resistance: 100 m
