AUTOMATIC

An automatic or self-winding watch features a winding mechanism powered by an oscillating mass on a rotor that turns with the movement of the wearer’s wrist. A clutch on the winding device prevents the system from overwinding the mainspring.

BALANCE WHEEL

The balance wheel oscillates (or vibrates) due to the hairspring. It provides exact and constant portions of time to the escape wheel through the pallet lever (see Escapement).

BEZEL

The ring that holds down the crystal of the watch. It can also be used for various timing functions, for example remaining air for divers or fuel reserves for pilots. Functional bezels rotate either unidirectionally or bidirectionally, sometimes on a clicking ratchet.

CALENDAR

Calendars are among the oldest horological complications. Some display the day of the week, month, year, or leap years. Related complications are day/night indications, and daylight saving. The most common manner of display is in a window on the dial (the information is on rotating disks), but creative watchmakers might put them on rollers, around the dial, or in a subdial. A perpetual calendar will account for leap years.

CHRONOGRAPH

A timing device that allows the user to start, stop and reset a separate hand to time a particular action. Subdials called totalizers or counters are usually used to display the counted minutes and hours as well as the watch’s own seconds function. (See also Fly-back chronograph and Split-seconds chronograph)

CHRONOMETER

A watch whose movement has been certified by the COSC (see COSC) following stringent pass/fail test in five positions and at three temperatures for a total of sixteen consecutive days. Seven different criteria are measured. A movement larger than 20 millimeters must have a deviance of no more than -4/+6 seconds a day; for a movement of 20 millimeters or less, the allowed deviation is -5/+8. After that, a watch can be called a chronometer. Some brands have their own certification, or choose not to be certified. There are also other agencies that certify chronometers (criteria may wary).

CONSTANT FORCE

Also known as a constant force escapement is any system that captures and compensates the mainspring’s diminishing energy as it unwinds, transferring it to the escapement to improve the watch’s accuracy by making the rate more even. One form is remontoir d’égalité, though it can take on many forms. The oldest may be the fusée, the latest is the silicon blade in the Girard-Perregaux Constant Escapement.

COSC

The Contrôle Officiel Suisse des Chronomètres (Official Swiss Chronometer Testing Institute) was founded in 1973 by the Federation of the Swiss Watch Industry and the Swiss cantons where watchmaking is a major industry. The COSC operates three control centers that test up to one million movements per year. See Chronometer.

CÔTES DE GENÈVE/GENEVA STRIPES

A traditional wave-like decorative pattern applied to movement parts. Mainly straight lines, but sometimes circular.

CROWN

The part of the watch used to wind up the mainspring and set the time or other functions. The crown was invented by Jean-Adrien Philippe of Patek Philippe in 1845 to replace key winding, which exposed movements to moisture and dust. Rolex popularized the screw-down crown,which enhances the water resistance of the watch, with its Oyster, released in 1926.

CRYSTAL

The “glass” used to cover dials is called a crystal, but it is made of various materials. The most popular on mechanical watches is sapphire crystal, a synthetic corundum made of aluminum oxide (Al2O3). Only a diamond is harder than corundum, making it exceptionally scratch-resistant. Other materials are mineral glass and Plexiglas ®.

DIGITAL

Digital displays are not only a feature of quartz watches. Numerals can be printed on disks and shown in an aperture on the dial similarly to the date window, or can be shaped by complicated mechanical means.

ESCAPEMENT

This core regulating mechanism in the watch consists mainly of the pallet fork, pallets and escape wheel. The energy created by the mainspring is led through the gear train to the escape wheel, which, with the help of the pallets pushing and pulling, portions the energy at a theoretically even rate. The escapement has been consistently developed and improved upon since the Middle Ages, when Dutch mathematician and physicist Christiaan Huygens invented the balance spring to replace the pendulum, essentially allowing portable, wearable timekeeping.

FLY-BACK CHRONOGRAPH

A type of chronograph that allows the user to press one pusher to instantaneously restart the chronograph, without the intermediate step of stopping the chronograph timing.

FUSÉE

The fusée is a conical pulley (fusée is French for rocket, a reference to the device’s silhouette) connected to the barrel spring by a chain or belt. As the barrel turns, the chain unravels from the narrow top to the wider bottom, thus compensating for the waning power in the spring. This ingenious but bulky mechanism went out with the pocket watch but has been revived in recent times by brands such as Breguet and A. Lange & Söhne.

GMT

Greenwich Mean Time was established in 1884 as a reference for all time zones in the world. In its simplest form, the GMT complication features one 12-hour hand, e.g., the home time, and a second 24-hour display, like a second row of numerals on the bezel or on the dial that can be set to destination time or another known place. The 24-hour display allows the user to determine whether it is night or day.

GUILLOCHÉ

An engraving technique used to create patterns on dials and usually done by hand using a stationery tool on high-end watches. When coated in enamel, the guilloché is referred to as flinqué.

HAIRSPRING

The fine spring attached to the balance wheel that makes it oscillate at a specific rate. It can be lengthened to slow down the beat or tightened to speed it up. Hairsprings nowadays are traditionally crafted in alloys such as alloys like Nivarox, but today an increasing amount of hairsprings are made of anti-magnetic silicon.

INCABLOC

A shock protection system named after the company that manufactures it. It is designed to absorb shocks that could damage the watch’s delicate balance assembly. Incabloc is one of a number of shock absorbing systems invented since the eighteenth century.

JEWEL

The shafts (arbors) that hold the wheels (gears) of a watch in place would wear out quickly were it not for jewel bearings, which minimize undue friction and reduce the need for lubrication. They have been used since the early eighteenth century. Watchmakers today use artificial rubies made from synthetic corundum. Jewels are used as ordinary bearings, but also as capstones, endstones and pallets.

MAINSPRING

The power at the heart of every mechanical watch, the mainspring consists of a spring of steel wound around an arbor and enclosed in a narrow cylinder or “barrel” ringed with gear teeth. As the spring unwinds, it turns the barrel, which powers the watch.

MECHANICAL

A mechanical movement is one driven by the energy released from an unwinding spring, known as the mainspring. The mainspring is usually wound by hand. In automatics, it is also wound by the action of a weighted oscillating rotor.

MINUTE REPEATER

Minute repeaters were originally created to tell time in the dark, or to aid blind people. Plain repeaters strike the hours; minute repeaters strike the hours, quarter hours, and minutes on demand, on up to three gongs. This complex mechanism must fit into a small case and sound without using too much power; arguably this complication is the hardest one to make.

MOON PHASE

This popular complication shows the phases of the waxing and waning moon. The moon surrounded by stars is usually on a disc and displayed in an aperture on the dial. As the moon revolves around the earth in 29 days 12 hours, 43 minutes and some, a normal moon phase uses a 59-tooth wheel, which needs to be adjusted for deviation every two years. A moon phase using a wheel with 135 teeth must only be adjusted every 122 years.

OSCILLATION

The to-and-fro movement of the balance wheel and hairspring assembly that allows time to be portioned out into controllable packets.

POWER RESERVE

The power reserve is the amount of energy still available in the mainspring – or any spring that drives a mechanism. How to indicate the power reserve often sparks the creativity of the watchmakers, but the most common mechanism uses a small hand on the dial of the watch.

QUARTZ

Quartz vibrates when a current is passed through it. The exact frequency (see VPH) can be defined by the way the crystal is cut. Quartz is also very resilient and, if thermocompensated, unaffected by temperature changes. A German engineer working in the U.S.A., Jürgen Staudte, invented the process for manufacturing quartz oscillators cheaply for many electronic devices, including watches.

RETROGRADE

The term means “moving backward” and refers to a display of time on a finite line. When the last digit has been reached (e.g, 12 o’clock for an hour hand), the hand returns the same way it came to the point of departure. The retrograde can be used for seconds, minutes, hours, dates or any other function.

ROTOR

The weight that swings with the wearer’s kinetic motions to wind the mainspring of an automatic movement.

SCREW-DOWN CROWN

Sometimes also screw-in crown, this system ensures that a movement is sealed off from water. The crown is designed like a threaded cap that has to be unscrewed before the watch can be wound or set by pulling out the stem in the usual manner.

SMALL SECONDS

A smaller counter or subdial on the dial showing the seconds function. This can be for aesthetic purposes or to make way for a chronograph hand that requires the full dial.

SPLIT-SECONDS CHRONOGRAPH

This complication starts two chronograph hands at the same time. A pusher can be used to stop, reset and restart one of them, while the other continues timing. This type of chronograph is also called rattrapante.

TACHYMETER

Scale on a chronograph’s dial or bezel that allows the user to calculate the velocity of vehicles like aircrafts and race cars. A tachymeter can also be used to calculate any countable units over a fixed time interval such as manufacturing quantities or production units.

TOURBILLON

Louis-Abraham Breguet is credited with the idea of placing the escapement inside a rotating cage to counter the effect of gravity that occur as pocket watches are generally always held in the same vertical position inside the pocket. Today the impact of the tourbillon remains disputed, since wristwatches are continually moving on the wrist in different positions. However, this bit of technical wizardry has become a common feature of highest-end watches. Some watchmakers even produce watches with multiple, differential-connected tourbillons that revolve at different rates like Greubel Forsey), or tourbillons that turn on two and three axes.

VPH

The number of times the balance wheel goes in one direction or the other is given in vibrations per hour (vph) or beats per hour (bph). These are also called half-oscillations or alternations. Balances commonly beat at 18,000, 21,600, 28,800, and a few at 36,000 and 72,000 vph and even higher. Oscillations are also given in Hertz (Hz), which is vhp divided by 3,600 (seconds) divided by 2; 28,800 vph = 4 Hz.X