Your basic wristwatch tells you the time.

But many wristwatches come with features that also display the date or even the phase of the moon. These little extras on wristwatches are called “complications.”

In horology, a complication refers to any feature in a mechanical timepiece beyond the simple display of hours and minutes. A timepiece indicating only hours and minutes is otherwise known as a simple movement. Common complications in commercial watches are day/date displays, alarms, chronographs (stopwatches), and automatic winding mechanisms.

The more complications in a mechanical watch, the more difficult it is to design, create, assemble, and repair. These stipulations do not apply or refer to quartz watches. A typical date-display chronograph may have up to 250 parts, while a particularly complex watch may have a thousand or more parts. Watches with several complications are referred to as grandes complications.

The initial ultra-complicated watches appeared due to watchmakers' ambitious attempts to unite a great number of functions in a case of a single timepiece. The mechanical clocks with a wide range of functions, including astronomical indications, suggested ideas to the developers of the first pocket watches. As a result, as early as in the 16th century, the horology world witnessed the appearance of numerous complicated and even ultra-complicated watches.