A complication is anything a watch does beyond telling the hours, minutes, and seconds. Every complication adds to the price and to the cost of servicing, but they are also delightful. Choose wisely.
A simple date shows the day of the month. You correct it by hand after every month shorter than 31 days.
An annual calendar handles 30-day and 31-day months on its own, so you correct it once a year, at the end of February. Some show days of the month around the edge with a special long hand; others show days of the month in a window.
A perpetual calendar also handles February and leap years, and it needs no correction until 2100. Most perpetual calendars show the day of the week and the month too. A few come with an extra piece to be installed in early 2100.
A leap-year indicator shows where you are in the four-year cycle, so you can set a perpetual calendar correctly after it stops.
An AM/PM indicator shows whether the hands mean morning or evening. On a calendar watch, it keeps you from setting the time 12 hours off, which would make the date change at noon instead of midnight.
If a calendar watch stops, you have to reset every display. Wind it regularly, or keep it on a winder if it winds automatically. On most calendar watches, don’t set the date between 10 p.m. and 3 a.m. The watch is moving the date then, and setting it by hand can damage the calendar.
A moon phase shows the phases of the moon, from new to full and back, on a small turning disc. A standard moon phase gains a day about every two and a half years, and you correct it with a small pusher or the crown. A precision moon phase stays within a day for 122 years or more. In my experience, people like the look of the moon, but they don’t keep it congruent with the actual moon phase.
A GMT watch shows a second time zone with either a) an extra dial or b) an extra hour hand that circles the dial once a day against a 24-hour scale, so you can tell whether it’s day or night at home. Some GMT watches let you move the main hour hand an hour at a time when you reach a new time zone, without stopping the watch. Any watch with names of cities around the bezel is a GMT.
A striking watch sounds the time by hitting tiny wire gongs coiled around the movement.
A repeater strikes the time when you pull a slide or push a button on the side of the case. On most repeaters, pulling the slide winds a small spring that drives the hammers when you let go.
A sonnerie strikes the hours and quarters by itself as they pass, and most also repeat on demand. A switch selects grande sonnerie, petite sonnerie, or silence. The chimes need their own mainspring, and on many sonneries you wind it by turning the crown backward.
A musical watch plays a short tune instead of striking the time. A separate spring drives it, and only a few makers build them.
An alarm watch has a mechanical alarm that buzzes or chimes at the time you set (generally on the next pass, no AM/PM). You wind the alarm separately, usually with a second crown. They used to be popular. Now that people have mobile phones, alarm watches are rare.
This table shows the tones each kind strikes.
| Complication | Hours | Intervals | Minutes |
|---|---|---|---|
| Hour repeater | Low tones (on demand) | None | None |
| Quarter repeater | Low tones (on demand) | Dual tones (15-minute blocks) | None |
| Five-minute repeater | Low tones (on demand) | Dual tones (5-minute blocks) | None |
| Decimal minute repeater | Low tones (on demand) | Dual tones (10-minute blocks) | High tones (single minutes) |
| Minute repeater | Low tones (on demand) | Dual tones (15-minute blocks) | High tones (single minutes) |
| Passing chime (en passant) | Single strike (on the hour) | None | None |
| Petite sonnerie | Low tones (on the hour only) | Dual tones (only at :15, :30, :45) | None |
| Grande sonnerie | Low tones (on the hour, and again with each quarter) | Dual tones (at :15, :30, :45) | None |
Take three o’clock. At 3:00, a grande sonnerie strikes three low tones. At 3:15, it strikes the three low tones again, then one dual tone for the quarter. At 3:30 and 3:45, it strikes the hour again, then two and three dual tones. A petite sonnerie strikes the three low tones only at 3:00, and at the quarters it strikes just the dual tones.
The case amplifies the gongs, so the metal changes the sound. Steel and titanium ring loudest and brightest. Gold absorbs some of the high notes and sounds warmer. Platinum absorbs the most, so platinum repeaters chime the quietest.
The sun reaches its highest point at a slightly different clock time each day. Over a year, sun time ranges from about 14 minutes behind clock time to about 16 minutes ahead. An equation of time shows that gap on the dial, and a few watches show sun time with a second minute hand.
In a tourbillon, the parts that keep time turn inside a small cage, usually once a minute. Breguet patented it in 1801 for pocket watches, which stayed upright in a pocket all day and lost accuracy to gravity. A wristwatch moves all day, so a tourbillon adds little accuracy. Most makers show the tourbillon through an opening in the dial, so you can watch it turn. A hidden tourbillon is a waste of money.
A flat tourbillon turns on one axis, in the plane of the dial, generally once a minute.
A 3D tourbillon, such as Jaeger-LeCoultre’s Gyrotourbillon, turns on two or three axes at once and costs far more.
A chronograph adds a stopwatch to the watch. One pusher starts and stops it, and the other sets it back to zero. Small dials count the minutes and, on many chronographs, the hours.
A flyback resets and restarts with a single push.
A split-seconds chronograph has two seconds hands, so you can time two runners who start together.
A power-reserve indicator shows how many hours the watch has left before it stops. Most watches keep going two to three days on a full wind, and some last a week or more. The indicator helps most on a hand-wound watch, because it shows you when to wind.
A twin-barrel watch has two mainsprings instead of one. The second spring keeps the watch going longer on a full wind and gives it steadier power as it winds down. The Lange 1 uses two to reach three days, and many watches that last a week or more use two or three.
A mechanical watch keeps time with a small wheel that swings back and forth, and each swing makes one tick. Watchmakers count those ticks in beats per hour. Most modern watches beat 28,800 times an hour, eight times a second, so the seconds hand moves in eight tiny steps each second.
A high-beat watch ticks 36,000 times an hour. At ten ticks a second, its seconds hand sweeps more smoothly. Zenith’s El Primero and Grand Seiko’s Hi-Beat models have beaten this fast for years, and Rolex joined them with the Land-Dweller in 2025. A faster beat keeps time a little better when you move around, but the parts wear faster and need servicing sooner.
Zenith’s Defy Inventor beats far faster, 129,600 times an hour, or 36 times a second.
TAG Heuer’s Mikrotimer beats faster still, 3.6 million times an hour, but only its stopwatch beats that fast, timing to a thousandth of a second. TAG Heuer made 11.
A world-time watch shows the hour in cities around the world at once, usually 24 of them. A ring of city names circles the dial, and a 24-hour ring beside it turns once a day, so you read each city’s hour next to its name.