Measuring devices on watches indicating things other than hours and minutes of current time, such as day, date, month, moon phases, chronometer subdials, power reserve, rotating bezel, heart rate, tides, compass direction, water depth, barometric pressure, altitude, speed (tachymeter), air temperature, etc.
A watch with other functions besides timekeeping. For example, a chronograph is a watch complication. Other complications coveted by watch collectors include: minute repeater, tourbillon, perpetual calendar, or split second chronograph.