A complication is any function on a watch other than the display of the time. Complications can range from the very simple and commonplace to extremely rare works of high horology that combine numerous functions and can take years to create. They include:

A chronometer is a watch that is certified to be exceptionally precise.

A chronograph is a watch that has a stopwatch built into the movement.

A Tachymeter measures units per hour, generally miles or kilometers. In order for a tachymeter to work, you must move at a fixed rate of speed and distance (e.g., 1 mile or 1 kilometer).

A Tachymeter is an instrument for measuring speed that is commonly found on watches. Typically, a scale is placed on the outer or inner bezel of a watch and is generally only found in conjunction with chronographs.

It’s easy to tell if a chronograph is a rattrapante; it will have three pushers on the case. It also has two second hands on the chronograph, one right on top of the other.

The Flyback chronograph is specially engineered so that when a second button is pushed while the chronograph is running, all the counters reset and immediately start again from zero. This feature was originally designed for pilots where split second accuracy is necessary for precise navigation. Flybacks are the exception, not the rule.

Originally, all chronographs were “monopoussoirs.” The two-button chronograph was not introduced until 1923 by Breitling. The difference between a one and two button chronograph is that the one button model cannot measure interrupted time spans.

Following date complications, the chronograph is the most common complication: a watch that has a stopwatch built into the movement.

Dual Time Zone (Travel Complications)

Dual Time Zone complications help determine the time in another time zone.

Dual Movement

While not technically a complication, the dual movement is a watch that contains two separate movements, each running from their own power source and each set independently.

Dual Time

In dual time watches, both displays are powered by the same movement.

GMT (Greenwich Mean Time)

The watch displays two or more time zones.

GMT (Greenwich Mean Time) with Independent Hour Hand

This variety of GMT is a further development of the original. What makes it different is that the regular hour hand is set independently of the 24 hour hand, which completely changes the functionality of the watch.

GMT (Greenwich Mean Time) with Fixed Hour Hand

Introduced by Rolex in the 1950's, this GMT complication is considered a pilot's watch. Its unique additional hour hand makes one revolution around the dial per day; pointing to twelve indicates midnight and pointing to six indicates noon.

World Time Zone

The World Time Zone feature has a rotating inner bezel with 24-hour display, part of the watch movement, and an outer bezel, listing the major cities in each of the 24 time zones. The outer bezel is set by the user. The inner bezel, marked to 24, makes one complete revolution per day.