The integrated Saros system
Beyond the GMT-function, the Sky-Dweller offers an integrated annual calendar, which automatically distinguishes between months that hold 30 or 31 days. Thus, the Sky-Dweller only requires one date adjustment per year - on the 1st of March.
The design mechanism for the annual calendar is exceptionally simple. Compared to traditional calendars with automatic time displays, only four additional gear wheels are needed for the Sky-Dweller. Rolex calls this valuable addition the Saros system, with reference to the ancient 18-year-cycle of the sun, moon, and earth. The months are displayed on the outer edge of the dial in 12 discreet apertures and the current month is highlighted in a contrasting colour.