In the past half-century, since it launched its GMT-Master, Rolex has brought out just two new complications: the Rolex Yacht-Master II, in 2007, with a countdown yacht timer, and the Rolex Sky-Dweller, equipped with both a second time zone and an annual calendar, in 2012. In this feature from our Baselworld 2012 issue, we explain how the Sky-Dweller, and its innovative movement, work.
The Rolex Sky-Dweller contains a new caliber, 9001, which Rolex makes in house. The second time zone is indicated by an off-center, rotating 24-hour disk. Local time, indicated by the center- mounted hands, can be adjusted quickly when you change time zones by setting the hour hand forward or backward in one-hour increments. The minutes, seconds, and second-time-zone indicators are not affected during this operation.
The calendar mechanism, which changes instantaneously (an annual calendar automatically differentiates between months of 30 days and 31 days, and need be adjusted just once per year, at the end of February) is relatively simple, Rolex says: the company has added just two gear ratios and four gear wheels to its existing instantaneous date calendar. As Rolex explains it, “The mechanism is designed around a fixed planetary gear wheel at the center of the movement. A satellite wheel engages with the planetary wheel and rotates, orbiting the planetary wheel in one month, driven by the date disk. The satellite wheel is fitted with four fingers for the four 30-day months (April, June, September and November). Click on watch photos for larger images.
“The gear ratio between the satellite wheel and the planetary wheel is calculated in such a way that at the end of each 30-day month – and only in these months – one of the satellite’s fingers receives an additional impulse from the date-change mechanism. This makes the calendar disk jump two days (from the 30th to the first) within a few milliseconds to display the correct date.” Rolex has dubbed the mechanism “Saros,” a Greek word that refers to the approximately 18-year cycle that can be used to predict when eclipses will occur. Rolex chose the name because it brings to mind the revolutions of the Earth and moon, which are like the motion of the satellite wheel (the Earth) with its four fingers (the moon).
The Rolex Sky-Dweller calendar has an unusual month display. The hour numerals correspond to the 12 months of the year. Next to each numeral is a window. The window for the current month (e.g., “IIII” for April,) is black; the other 11 windows are white. (On the brown-dial model, the correct month is indicated by a white window for better contrast.)