A watch complication is any function in a timepiece beyond the simple display of hours, minutes, and seconds. Common examples include date displays, chronographs, moon phase indicators, and alarm functions. The more complications a watch has, the more complex its movement becomes, often requiring exceptional craftsmanship and engineering.

A perpetual calendar is one of the most sophisticated watch complications. It automatically adjusts for the varying lengths of months, including leap years, and typically displays day, date, month, and moon phase. Unlike annual calendars, perpetual calendars don't require manual adjustment until the year 2100 (due to the Gregorian calendar's leap year rules).

A chronograph is essentially a stopwatch function built into a timepiece. It typically features pushers on the side of the case to start, stop, and reset the timing function without interfering with the watch's normal timekeeping. Chronographs often have sub-dials to display elapsed minutes and hours, and some advanced versions include flyback or rattrapante (split-seconds) functions for more precise timing.

Invented by Abraham-Louis Breguet in 1795, the tourbillon is a mechanism that counters the effects of gravity on a watch's accuracy. It mounts the escapement and balance wheel in a rotating cage, typically making one full rotation per minute. This continuous rotation averages out positional errors that occur when the watch is in different orientations. While less critical in modern wristwatches (which change position frequently), the tourbillon remains a showcase of horological mastery and craftsmanship.

A moon phase complication displays the current phase of the moon as it appears in the sky. It typically features a rotating disc with two moons that moves behind an aperture on the watch dial, completing a full cycle every 29.5 days. This is one of the most poetic and aesthetically pleasing complications, often beautifully decorated and adding artistic value to the timepiece.

Both are acoustic complications that chime the time, but they differ in complexity: minute repeaters chime the hours, quarters, and minutes on demand when a slide is activated. A grand sonnerie (French for "grand strike") is much more complex—it automatically chimes the hours and quarters at every quarter hour, and can also strike on demand like a minute repeater. The grand sonnerie is considered one of the most challenging complications to create.

A GMT complication allows the watch to display time in two different time zones simultaneously. It typically features an additional hour hand that completes one rotation every 24 hours, along with a 24-hour scale on the bezel or dial. Originally developed for airline pilots, GMT watches have become popular among frequent travelers and international businesspeople.

Not necessarily. While some complications like the tourbillon are designed to improve accuracy, most complications add functions rather than enhance timekeeping precision. In fact, highly complicated watches can sometimes be less accurate due to the increased energy demands and complexity of their movements. The primary value of complications is their demonstration of horological artistry, craftsmanship, and engineering innovation rather than timekeeping performance.