The TONDA PF Gregorian Annual Calendar 42mm case houses one of the most poetic complications in Haute Horlogerie. The Caliber PF339 displays a retrograde date, day, and month along with a moonphase with a precision of 122 years in both hemispheres.

These astronomical and calendar functions complement the traditional indication of hours, minutes, and seconds, providing an abundance of information that nevertheless adheres to the aesthetic purity the Maison has demanded for this champion of the mastery of time.

The genius of the retrograde annual calendar is in its mechanism, which requires only one adjustment per year. The date automatically adjusts to changes in the number of days in each month – 30 or 31 days – but counts 29 days for the month of February regardless of the year. Only once at the end of February in leap years, which occur every four years, does the wearer of the TONDA PF Gregorian Annual have to set the date manually. It then continues flawlessly for the next 365 days.

The moonphase of the TONDA PF Gregorian Annual complements its date display. It is called a “precision moon” because it requires correction only every 122 years. This remarkable accuracy involves compensating for the gap between a classic lunar cycle (29 days and 12 hours) and the actual lunar cycle (29 days, 12 hours, 44 minutes and 2.8 seconds). Poetically evoking a sparkling galaxy filled with stars, the solid rose-gold moon counter and moon pastilles appear against an aventurine glass sky.