A Vacheron Constantin is the World's Most Complicated Watch.

THE FIRST CHINESE PERPETUAL CALENDAR
Humans soon began to become aware of the concept of time, particularly by observing the alternation of day and night, the cycle of the seasons, and the movements of the Sun and Moon. However, it was not until the advent of writing-in the 4th millennium B.C. in the West and the 2nd millennium B.C. in China-that time became predictive. From that time on, calculations based on astronomical observations were used to make a calendar. The ancients developed different calendar systems, based on lunar months (Islamic calendar), the solar year (Gregorian calendar) or a combination of the two, i.e., lunisolar calendars with the necessary adjustments to match them. The Chinese calendar, like the Greek, Jewish and Celtic calendars, falls into the latter category.

A complex and irregular system

The months of the Chinese calendar are lunar and begin with the new moon day calculated on the 120th meridian east (UTC +8h) passing through the Shandong Peninsula and Hangzhou city. To comply with the average length of a lunation (29.53 days), the months are composed of 29 or 30 days. Altogether, however, the 12 lunar months form a year 11 days shorter than the solar year (365.2422 days). For this reason, the Chinese calendar inserts an intercalary or embolismic 13th month (embolismal: in the Greek, Julian and Hebrew calendars, it is said to be an added month to reestablish the correspondence between the lunar and solar years) every two or three years, that is, six times during a 19-year metonic cycle. The latter-so named by the Greek astronomer Meton (5th century BC)-is based on the observation that 19 solar (or tropical) years correspond almost exactly to 235 lunar months and 6,940 days. Depending on the lunations, the common Chinese year can therefore have 353, 354 or 355 days, while the embolismic year has 383, 384 or 385 days. The other factor to consider is the Chinese New Year, whose date marks the beginning of the lunar year but fluctuates between January 21 and February 21.
The solar year of the Chinese calendar is an effective tropical year, calculated on the same meridian (120th meridian east) between two winter solstices. It is divided into 24 periods of 15° each along the ecliptic, which is the apparent path the Sun takes in a year relative to the Earth. Each period, also known as jie (knot) and qi (breath of life), lasts about 15 days: an average length that corresponds fairly accurately to the Gregorian calendar, that is, to a 365- or 366-day year.

Another feature of the Chinese calendar is that units of time are numbered according to the association of two sets of signs-10 heavenly logs and 12 earthly branches-for a total of 60 different possible combinations. Typically this cycle, called sexagesimal, is used to mark the passage of years, but it can also be applied to months, days or hours. The trunks are associated with the five elements (wood, fire, earth, metal, water) and a polarity (yin, the feminine principle or yang, the masculine principle). The branches are represented by the 12 signs of the Chinese zodiac in the following order: mouse, ox, tiger, rabbit, dragon, snake, horse, goat, monkey, rooster, dog and pig. At each stage of the calendar, the trunk number and branch number are incremented by one to create a cycle of 60 combinations corresponding to the lowest common multiple of 10 trunks and 12 branches or animals of the zodiac.

Lunisolar calendars play with complementarity. In order to establish the dates of leap moons and the beginning of lunar years and, therefore, achieve perfect synchronization, it is necessary to know the solar calendar. The Chinese continued to improve their calendar so that it reflected the reality of astronomical phenomena as closely as possible. The resulting precision, however, is an element of complexity, because it involves modeling a system that is essentially based on irregularity.
Although it has been possible to program the calculation of the Chinese calendar since 1645 using analytical theories, as scientists have done, making a mechanical application has been an inscrutable challenge.

A world first

The main innovation of Les Cabinotiers - The Berkley Grand Complication is the traditional Chinese calendar. It is the first timepiece to present it in the form of a perpetual calendar, with all the calculation, patience, ingenuity and understanding of Chinese culture that this entails.

Concretely,first the three watchmakers had to work out the calendar in the form of algorithms, which they then transcribed into a mechanism programmed up to 2200 capable of following the irregularities of a calendar whose lunar years and months have different durations on a sequential basis, with the first day of the year fluctuating. To achieve this, they devised three mechanical "brains" capable of controlling the cams and gears of one of the two additional movement mechanisms on the front side. In principle, each mechanism "drives" a calendar component: the lunar cycle, the solar cycle, and the metonic cycle, which lasts 19 years, indicated by so-called golden numbers, and is visible in the counter at 3 o'clock.

In addition to programming the timepiece back to 2200, the watchmakers at Vacheron Constantin were able to make a disc display of the exact-but by definition variable-date of the Chinese New Year. This is another major achievement because this date, so important in Chinese culture, fluctuates between January 21 and February 21 each year.

The front side of the clock is essentially devoted to the different indications of the traditional Chinese calendar. To orient oneself, one must first determine whether the current year is normal or embolismic (opening at 11 o'clock) and whether the month is a short or long lunar month (opening at 12 o'clock on the New Year's hard disk). This perpetual calendar with Chinese characters presents the date display with pointer on the counter at 6 o'clock, while the day is displayed at 8 o'clock and the month at 4 o'clock.

Les Cabinotiers - The Berkley Grand Complication also indicates an unprecedented amount of information related to the sexagesimal cycle, the keystone of the Chinese calendar and the entire cosmological model of that culture. An even more extraordinary achievement when one considers that the information displayed refers to different time scales: the hour, the day and the year. Vacheron Constantin's watchmakers integrated a jumping display of the 10 celestial logs, with yin-yang polarity and day-related elements (counter at 9 o'clock). The counter at 3 o'clock shows the 12 terrestrial branches associated with the double hours; each day is divided into 12 two-hour segments starting at 11 o'clock. The display is continuous and divided into 24 hours. Finally, in an aperture below the moon phases, the profile of the current year's Chinese zodiac animal appears. The combination of the animal and the celestial trunk suggested on the New Year's disc indicates the position within the sexagesimal cycle.

The Chinese perpetual calendar is complemented by the precision phases and age of the moon, visible on the counter at 12 o'clock, which do not need correction for as many as 1,027 years. The final special feature of the Chinese perpetual calendar is the indication on the side of the caseback - by a central hand - of the 24 solar periods of the agricultural year, accompanied by the length of the months, seasons, solstices and equinoxes