ALARM

A pocket watch, wristwatch or clock that automatically sounds at a preset time.

ALTIN

A hard coating consisting of the metallic elements aluminium and titanium, and nitrogen. Used to cover metals for a black scratch resistant coating.

ANALOGUE

An analogue watch displays time by means of hands and a dial (as opposed to digital or alphanumerical).

ANNUAL CALENDAR

A full or partial simple calendar that takes automatically into account months with less than 31 days or leap years, but not of leap years. It must be adjusted once a year.

ANTI MAGNETIC

Describes a watch that is protected against magnetic fields.

ARABIC NUMERALS

1, 2, 3, etc. Arabic numerals, which were widely used on watch dials towards the eighteenth century, allow greater scope for fantasy than their Roman counterparts.

ATM (ATMOSPHERE)

Unit of measure to indicate a watch's water-resistance, specifically its capacity to resist pressure, based on standard atmospheric pressure defined as 101.325 kilopascals (kPa) equivalent to approximately 1 bar. Can be expressed in different ways: 10 atm = 10 bars = 100 metres

AUTOMATIC (SELF-WINDING)

Describes a mechanism that winds the mainspring by using the movement of the arm to cause a rotor to rotate and which, via specific gears, winds the mainspring.

BAGUETTE

The cut of a gemstone stone that has been cut into a long, rectangular shape.

BALANCE SPRING

Very fine spring and the "heart" of a mechanical watch. Its ends are affixed to the balance and the balance-cock. Its elasticity allows the balance to make regular oscillations. Its length, and the balance's moment of inertia, determine the duration of each oscillation. Its length can be altered to regulate the watch.

BARREL

A cylindrical box (the barrel) and toothed disc (wheel), protected by a cover. The barrel, which contains the mainspring, turns freely on its arbor. The mainspring is hooked to the barrel at its outer extremity and to the arbor at its inner extremity. The barrel wheel meshes with the first pinion of the geartrain. As it slowly rotates, its arc varies from one-ninth to one-sixth of a revolution per hour. A hanging barrel (also known as a standing barrel or floating barrel) is one whose arbor is supported at the upper end only, being attached to the barrel bridge with no support from the lower plate.

BATTERY

A device that transform the energy created by a chemical reaction into electrical energy. Typically, a battery lasts for two to five years. Its lifespan will depend on the type of watch, its size and the amount of energy required for the different functions. A chronograph will consume more energy than a watch that shows only hours, minutes and seconds.

BEZEL

A ring around the case middle that secures the crystal.
A rotating bezel records additional information such as the duration of a given phenomenon.
The bezel on a diving watch is unidirectional. This is a deliberate feature and an additional safety factor as the bezel only rotates in the direction that will reduce dive time. Hence if the bezel is accidentally turned, the diver can still surface with sufficient air and respect decompression stops.

BRIDGE

A metal plate under which the pivots of the wheels and pinions turn.

BRILLIANT CUT

A round diamond that is cut with 57 or 58 facets or 32 facets + plus the largest facet called the table, 24 are below. The 58th facet is optional and is polished at the point of the diamond.

CABOUCHON

A polished precious or fine stone cut into a dome and without facets.
Used to decorate a watch dial and sometimes the crown.

CALIBRE

Used to denote the layout and dimensions of the different movement pillars, wheels, barrel, etc. ""calibre"" has been used to indicate the shape of the movement, its bridges, the origin of the watch, its maker's name, etc.
Now designates the movement itself.

CARAT

When abbreviated (ct.) a carat is a standard unit of weight used for gemstones.
1 carat weighs 0.2 gram (1/5 of a gram). 
A hundredth of a carat is called a point.

CARBON FIBER

Is a material consisting of fibers composed mostly of carbon atoms. The carbon atoms are bonded together in crystals that are more or less aligned parallel to the long axis of the fiber. The crystal alignment gives the fiber high strength-to-volume ratio (making it strong for its size). Several thousand carbon fibers are bundled together to form a tow, which may be used by itself or woven into a fabric.

CASE

Container that protects the watch movement from dust, damp and knocks.
The case is part of the watch's appearance and, influenced by fashions and buyers' personal taste, must have visual appeal. The main parts of a Lépine pocket watch case are the middle, inside which the movement is secured, and the case-band. On the bridge side, the middle of the case is closed by the back cover (sometimes with a second cover inside called a cuvette). On the dial side it is closed by the bezel that secures the glass.

CERAMIC

From the Greek keramos meaning fired pottery. In watchmaking, ceramic is a high-tech material, generally made from aluminum and zirconium oxides for the manufacturing of cases and decorative elements.

CHIMES

The quarter-hours are sounded on three, four or more gongs with different pitches, the best-known being the Westminster chimes.

CHRONOFIABLE

A joint certification project by a consortium of watch companies which accelerates the watch's ageing process by a factor of eight to simulate the effects of six months' wear in three weeks. The majority of leading watch brands submit watches for testing and are issued with a Chronofiable certificate.

CHRONOGRAPH

A watch indicating hours, minutes and seconds combined with a mechanism whose hand can be started, stopped and returned to zero on demand to measure a duration to one fifth, tenth or even hundredth of a second. Subcounters for the minutes and hours (usually 30 minutes and 12 hours) totalise the number of revolutions by the chronograph hand. The accuracy of these recorded times can only be guaranteed if the chronograph has satisfied the criteria of the ""chronometer"" label.

CHRONOMETER

A chronometer is, etymologically, an instrument for measuring the time. With usage it has come to mean a high-precision watch displaying seconds whose movement has been controlled over a period of several days, in different positions and at different temperatures, by an official neutral body. Only mechanisms that have satisfied the criteria for precision of ISO 3159, or its equivalent, are issued with an official chronometer certificate.

COLUMN WHEEL

The wheel which coordinates the start, stop and return to zero functions of the chronograph hand.

COMPLICATION

Any function other than the indication of hours, minutes and seconds, regardless of whether the mechanism is hand-wound or self-winding, mechanical or electronic, and of movement height.
Complications were instrumental in the rediscovery of the watchmaker's art in the 1980s and have continued to play an important role in the development of the traditional wristwatch.

COSC

The COSC awards the title of ""chronometer"" to each watch whose accuracy and consistency of rate has been demonstrated over fifteen days of tests at one of the COSC's Bureaux Officiels (BO). Each watch is tested in five positions and at different temperatures. The COSC is a non profit association created by five swiss cantons, Bern, Geneva, Neuchâtel, Soleure, Vaud. Its headquarters are in La Chaux-de-Fonds. The BO are in Biel, Geneva and Le Locle.
A certificate is issued to an individual watch, not to a model or a range.

CÔTES DE GENÈVE

A decoration of undulating lines, like waves, frequently used to embellish superior quality movements.

CROWN

The winding crown is a knurled or fluted button of various shapes, held between the thumb and forefinger and used to wind the watch.

CRYSTAL

A thin sheet of glass or a transparent synthetic material to protect a clock or watch dial.

DATE

The number, in order, of each day in the month.

DAY

Period between the rising and setting of the Sun.
A 24-hour interval, determined by the Earth's rotation on its axis.

DAYLIGHT SAVING TIME

Period between the rising and setting of the Sun.
A 24-hour interval, determined by the Earth's rotation on its axis.

DIAL

A plate of metal or another material which, in a standard clock or watch, serves to indicate hours, minutes and seconds. Dials come in an almost limitless variety of shapes, decorations, materials, etc.

DIAMOND

Diamond is the hardest and most luminous precious stone. The price of a diamond is calculated according to the 4C criteria: Cut - Carat - Clarity - Color. The weight of a diamond is expressed in carat: 1 carat is equal to 0.20 gram. Pure colourless carbon, in jewellery the diamond is cut into facets to increase its sparkle. In watchmaking it is used to decorate straps, cases, bezels, etc.

DIGITAL

A system controlled by the watch movement to indicate the time.

DUAL TIME ZONE

Describes a watch that simultaneously gives the time in two time zones, usually local and the wearer's home.

EMERALD

The saturated green variety of the Beryl family. Its colour is due to minute traces of chromium or sometimes vanadium. Inclusions in emerald are called jardins from the French word for garden.

ENAMEL

A vitreous substance whose main component is silica mixed with oxides (transition metals) that create a vast palette of colours. Enamel is used to decorate metal surfaces, in particular gold, silver and copper.

ENGINE TURNING (GUILLOCHÉ)

A style of hand or machine engraving with intersecting wavy or straight lines. When the piece is moved horizontally or vertically against the tool, the finished effect is guilloché, compared with flinqué or flinking which follows a radial movement.

ENGRAVING

The art of forming patterns either by hand, using a graver, or by machine such as a rose engine.

EQUATION OF TIME

The equation of time is the difference between true solar time and mean time. True solar time, given by sundials, varies from day to day because of the Earth's elliptical orbit, and according to the longitude of the point of observation.
Mean time, given by watches, ignores these variations and for every day of the year mathematically divides time into equal hours. Four times a year, on April 15th, June 14th, September 1st and December 24th, true solar time and mean time coincide. On the other days, the difference ranges from minus 16 minutes and 23 seconds on November 4th, to plus 14 minutes and 22 seconds on February 11th.

ESCAPEMENT

A mechanism that is fitted between the gears and the regulating organ. Its function is to suspend the gears' motion at regular intervals and to supply energy to the balance.

FOLDING BUCKLE

An articulated buckle that unfolds when opened. Should the buckle accidentally come open, it will still hold the strap sufficiently in place to prevent the watch from slipping off the wrist.

FOUDROYANTE (JUMPING SECONDS OR HAND) (FLYING SECONDS)

On a chronograph, a hand that makes one rotation every second, pausing four, five, even eight times to indicate quarters, fifths or eighths of a second.

GOLD

Gold  has seduced the world with its beauty, but also because not even acid can alter its natural properties. An estimated 130,000 tons have been extracted from the earth since prehistoric times, of which 100,000 tons in the twentieth century alone. Gold is a malleable substance (with a hardness of just 2.5) and therefore easy to work with. It can be used in an alloy with other metals, often silver and copper. These alloys increase its resistance and change its colour.

GRANDE SONNERIE

Watch  that strikes the hours and quarters in passing and repeats the hour at each quarter. The hour and quarter strikes can be repeated on demand.

HAND

A variously shaped indicator made from a thin piece of lightweight metal and which moves round a dial, with or without graduations. Most watches have three hands, one each for the hours, minutes and seconds. Early watches only had one hand, for the hours.

HOROLOGY

The science of measuring time.

JEWELS

The international term for the jewels (rubies) in a watch movement that are used as bearings for pivots to reduce friction.

JUMPING HOUR

A means of display in which the hour, shown through an aperture, instantly changes every 60 minutes.

JUMPING SECONDS

On a chronograph, a hand that makes one rotation every second, pausing four, five, even eight times to indicate quarters, fifths or eighths of a second.

LEAP YEAR

Introduced by Julius Caesar in 45 BC as part of the Julian calendar, the leap year was already found in certain Egyptian and Babylonian calendars. It has 366 days and generally occurs every four years to take into account the time taken for the Earth to make one complete revolution of the Sun, i.e. 365.2422 days.

LUG

A thin metal rod fixed between the case horns for attaching the watch strap.

LUMINESCENT

Having the property to emit light rays. In watchmaking, Tritium is the name given to a radioluminescent substance containing tritium. It was used to coat numerals, markers and hands so they could be read in the dark.

MANUAL

Describes a movement that is wound by hand using the winding crown.

MANUFACTURE

The Swiss watch industry uses this term to differentiate between a company that manufactures a watch almost in its entirety as opposed to finishing shops which only assemble and time the watch, and fit the hands and movement, and établisseurs.

MECHANISM

A configuration of parts to perform a function.
The watch is a mechanism whose various parts are themselves mechanisms, each with a specific function.

Moonphases
A mechanism and display representing the different phases of the moon. A complete lunation takes 29 days, 12 hours, 44 minutes and 2.8 seconds and is divided into four phases. These are new moon, first quarter, full moon, last quarter.

MOONPHASES

A mechanism and display representing the different phases of the moon. A complete lunation takes 29 days, 12 hours, 44 minutes and 2.8 seconds and is divided into four phases. These are new moon, first quarter, full moon, last quarter.

MOVEMENT

The duly-assembled organs and mechanisms of a watch, meaning the winding and hand-setting mechanism, the mainspring, the gears, the escapement and the regulating organ (spring balance).

PERPETUAL CALENDAR

A watch whose perpetual calendar (see complication) automatically takes the number of days in the month into account: 30 or 31 and the 28 or 29 days of February for ordinary and leap years. Unless it takes into account century years that are not leap years, it will need adjusting in 2100, 2200 and 2300 but not in 2400. A 48-month dial, derived from pocket watches, corresponds to three ordinary years and one leap year. On the more legible 12-month dial, ordinary and leap years are shown by a hand or aperture.

PETITE SONNERIE

Watch that strikes the hours and quarters in passing without repeating the hours at each quarter.
The hour and quarter strikes can be repeated on demand if the subsidiary seconds are coupled to a striking mechanism.

PLATINUM

A heavy metal, greyish white, that is highly resistant to corrosion and difficult to work with.

POINÇON DE GENÈVE

A distinctive hallmark depicting the Geneva coat of arms, granted by an official body at the Ecole d'Horlogerie de Genève and placed on movements whose quality and finish conform to precise specifications.

POWER RESERVE

(Originally called Réserve de Marche) is a complication of the watch, which is designed to show the amount of remaining stored energy usually in either hours or days. The power reserve indicator indicates the tension on the mainspring at any particular moment.

QUARTZ

Quartz has the specific property of vibrating at a very high frequency (32 MHz) placed under electric current. Under certain conditions, it imparts its own vibration frequency to the circuit. This property has been used in electronic watches since the 1970s.

REPEATER

A watch that strikes the hour on demand by activating a pushpiece or a slide (bolt).

ROMAN NUMERALS

I, II, III, etc. Roman numerals have traditionally been used on clock and watch dials. IV is often given as IIII to create visual symmetry with the VIII. Only the IX is written using the subtractive principle.

ROTOR

A semi-circular disc that freely rotates with each movement of the arm to automatically wind the mainspring. Its own weight returns it to a vertical position.

RUBY

A very hard red stone that is a type of corundum (aluminium oxide). Ruby is especially suited to making bearings (jewels) for the watch's different moving parts and the organs of the escapement, thereby reducing friction to a minimum.

SAPPHIRE

Sapphire is a precious gemstone (a type of corundum) that ranges in colour from blue to pink to yellow to green to white to purple (mauve sapphire) to pink-orange (padparadscha sapphire). Six-sided asterisms sometimes occur in star sapphires (caused by inclusions of tiny, thin, parallel needles of rutile). Sapphires are related to rubies. Sapphire has a hardness of 9 and a specific gravity of 3.9 - 4.1. Sapphires are often heat treated to improve their colour.

SELF-WINDING (AUTOMATIC)

Describes a mechanism that winds the mainspring by using the movement of the arm to cause a rotor to rotate and which, via specific gears, winds the mainspring.

SIMPLE CALENDAR

Shows the date, i.e. the number, in order, of each day in the month. Certain simple calendars also display the names of the months. A simple calendar mechanism uses a single disc display, or two discs when it incorporates a Large Date function.

SKELETON

A movement whose plate and bridges have been cut away to expose the wheels, leaving only the substance which the watch needs to function. The movement is placed between two sapphire crystals to be seen.A movement whose plate and bridges have been cut away to expose the wheels, leaving only the substance which the watch needs to function. The movement is placed between two sapphire crystals to be seen.

SLIDE

In a repeater watch, a part made from the same metal as the case and which slides along the case middle to wind the spring of the striking mechanism. A silent-slide prevents the mechanism from striking.

SNAILING

A decoration of compact spirals on a dial, created using a rose engine.

SPLIT SECONDS CHRONOGRAPH

The split-seconds chronograph is used to time different events that begin but do not end together. When set, the hand of the chronograph and the hand of the split seconds button when the first event ends. After reading the intermediate time a second push on the button makes it catch up with the first hand and the two continue their movement together. At the end of the second event, the split-seconds hand is stopped again to read this second intermediate time, and so on. At the end of the last observed event, both hands can be stopped and returned to zero. One pushpiece operates the split-seconds hand only while the second pushpiece operates both hands.

SPRING

The source of mechanical energy in a watch. A strip of tempered blued steel or a special steel alloy, coiled inside the barrel.

STEEL

Iron mixed with a small amount of carbon. The majority of bracelets (straps) and cases use 316L surgical steel for its anallergic properties.

STRAP

A means of attaching the watch around the wrist. A strap can be in gold, silver, steel, leather, exotic skin, etc. and in styles from the simplest to the most elaborate.

TACHYMETER

An instrument for measuring speed.

TIMEZONE

In order to standardise time measurement in each country, since 1883 the Earth has been divided into twenty-four time zones, the first of which is intersected by the Greenwich meridian, which is the prime or zero meridian. Each point within a given time zone has the same legal time.

TOURBILLON

A system devised and patented by Abraham-Louis Breguet in 1801 to compensate for errors of rate caused by the Earth's gravitational force in upright positions. The escapement is mounted in a revolving cage with the regulating organ (balance) at the centre. The escape-wheel pinion turns about the fixed fourth wheel. The cage generally revolves once a minute and, in doing so, compensates for errors of rate caused by the vertical position in which pocket watches spend most of their time.
This delicate and complex structure is one of watchmaking's most ingenious mechanisms. A simplified and more robust alternative is the karussel where the cage is driven not by the fourth wheel but by the third wheel. A tourbillon can contain a lever or a detent escapement.

WATER RESISTANCE

A watches water-resistance is measured in bars (a unit of pressure where 1 bar equals 1 atmosphere or atm).
Manufacturers generally indicate this water-resistance in metres (m), feet (ft), or atmospheres (atm). A watch that is described as water-resistant, with or without an additional indication of overpressure, must be conform and tested to the criteria set out in NIHS 92-10 (equivalent to ISO-2281 international standard). These watches are destined for ordinary everyday use, including periods of immersion in water such as leisure swimming. They can be used in conditions of changing air pressure, water pressure or temperature. However, even with an overpressure indication they are not intended to be worn for underwater diving.
A diving watch is made to be worn underwater at a depth of at least 100 metres (330 feet). It must include a time control device and fully conform to the criteria set out in NIHS 92-11 standard (ISO 6425) in terms of luminosity, shock-resistance, anti-magnetism and the solidity of the strap.

WIND

The action of tightening the mainspring coiled inside the barrel by means of the winding crown (in a hand-wound watch ) or the rotor (in a self-winding watch).

WORLD TIME

Describes a watch  that indicates, usually by means of subdials surrounding the main dial , local time (true solar time) in different world cities. Often these cities were chosen for their political or economic importance prior to 1883 when universal time was introduced.