In watchmaking, a complication is any function other than the indication of hours, minutes and seconds. Complications are highly sought after by mechanical watch enthusiasts and there are many different kinds to choose from. A watch with many complications is a complex model that illustrates extraordinary watchmaking expertise.
The most common complications display the date and the day of the week. Meanwhile, the chronograph is used to accurately measure the duration of an event. A push-button, usually located at 2 o’clock, starts and stops the chronograph hand. And a second push-button, located at 4 o’clock, is for resetting. The GMT function, which stands for Greenwich Mean Time, allows you to display the time in two or more time zones, in addition to local time, using a second, independently adjustable, hour hand. Most mechanical movements can run for approximately 40 hours between windings. This is called the power reserve. The complication with the same name displays the running time before a watch must be rewound. This indication usually appears on the dial or on the case back and is shown via a hand, a disc or a linear display.
The calendar shows the date and day of the month (from 1st to 31st). Yet, there are several types of calendar complications:
The simple calendar automatically indicates the date by displaying the day of the month. When a month has fewer than 31 days, the date must be adjusted manually.
The annual calendar does not account for the month of February or leap years and must therefore be correctly manually once a year.
The perpetual calendar accounts for regular and irregular months (fewer than 31 days).
Watches with a moon phase complication have a sub-dial that shows the different phases of the Moon (new moon, waxing crescent, first quarter, etc.) over approximately 29.5 days. This complication is not necessarily very useful, but it is very poetic and aesthetic in appearance.
Also called a “rotating cage”, the tourbillon offsets errors of rate caused by the Earth's gravity when a watch is in an upright position. This system was patented by French watchmaker and physicist Abraham Breguet in 1801.
On this type of display, the hand moves across an arc instead of making a full rotation. When it reaches the end of the scale, it goes back to where it started. A retrograde display is primarily used on watches that indicate the day of the week, the month, the season or other kinds of information. The primary goal of this system is to create particularly original dials.