Mechanism in addition to the time display. For various displays and functions: chronograph, perpetual calendar.
- Perpetual calendar
- Reserve power indicator
- Moon-phase display
- Equation of time (Zeitgleichung)
- Astronomische Anzeigen
- big date
- Double chronograph
For an example of the rarest complications united in a wristwatch, see the "Sky Moon Tourbillon" by Patek Philippe. Note that this watch is on offer for sale, for a mere $1,100,000, so let me know if the link is no longer valid, and so presumed sold.