“It’s a combination of lunar and solar cycles that are not in perpetual synchronicity,” he said. “The years are not always the same length. They vary between 352 days and 355 days.
“The best we could do is break it down into cycles of 12, which means every 12 years, it needs an adjustment — we have to change one component, for the next sequence of 12 years. We do the first adjustment for free, so it will take you for the first 24 years.”
Unlike the Gregorian calendar, which has a name for each month and a number for each year, the Xiali calendar does the reverse, giving names to years and numbers to months. It is organized in cycles of 60 years that combine a cycle of 10 “Heavenly Stems” that include the seasons, plus five elements (water, wood, metal, fire and earth), the planets, colors, flavors and virtues. Factored into this are 12 “Earthly Branches” that correspond to the signs of the zodiac, each represented by an animal. For example, 2023 is the year of the rabbit and the element is water.
How is all of that reflected in the Tonda? The watch condenses it into a surprisingly readable layout — if you can read Chinese characters — including hours and minutes, the month and its length (29 or 30 days) along with its numbering system, the year’s animal and element, with alternating colors depending on whether it is an odd yin year or an even yang year.
Instead of four seasons, the Chinese calendar is organized into 24 sections corresponding to the sun’s trajectory as seen from Earth, displayed along the periphery of the watch dial.
“These cycles charted elements like rainwater level, the awakening of the insects, changes that happen every 15 days,” Mr. Terreni said. “It helped you to eat and nourish yourself with things that are in season. It helped optimize your health.” For good measure, the watch also numbers the days in the lunar cycle along with the moon phases.