Accuracy Watches and clocks are among the oldest and most precise mechanical devices. A movement that shows a 30-second departure from true time in a 86,400 second day has a mathematical error of 0.035%. In other terms, it is 99.965% accurate. Officially certified chronometers can achieve an error of less than 0.005%.

Adjustment  The fine-tuning of a movement in various positions and temperatures. There are various degrees of adjustment; an ordinary watch is timed crown up and dial up, and adjusted for a maximum rate variation of 30 seconds a day between the two positions. For precision adjustment the movement is timed in five positions and at three different temperatures, usually 4°, 20°, and 38°C.

Alarm  One of the earliest complications of mechanical timepieces, known since the 16th century. Today's wrist alarms can be automatic, manually wound or quartz regulated.

Amplitude  The maximum angle from dead centre described by a balance-wheel or pendulum.

Analogue indications The conventional way of showing the time with hands moving around the dial.

Annual calendar A watch showing the calendar without correction for a year, from 1 March to 28 February.

Anti-magnetic A watch is considered anti-magnetic if it continues to function in a magnetic field of 4800 A/m (Amperes per meter) with a maximum rate variation of 30 seconds a day. To this end, most of the essential components of the regulating organ (the pallet-lever, escape wheel, roller, balance-staff, wheel and spring) are made of metals that cannot be magnetized or only with difficulty. To increase resistance to magnetic fields, some manufacturers surround the movement with a shell of conductive metal, such as soft iron, which prevents magnetic fields building up inside it. Magnetized movements can be neutralized with the help of a degaussing coil.

AOPA AIRCRAFT OWNERS AND PILOTS ASSOCIATION

Aperture Where the date is displayed within the dial of the watch

Assay The quantitative analysis to determine the proportion of precious metals in an alloy.

Assembly  Putting together components into a functioning watch.

Atmosphere (Atm) A measure of the water resistance of a watch.

Automatic lathe A term describing a wide range of automatic machine-tools for milling preliminary watch parts.

Automatic winding  A device which uses the motions of the wrist to wind the mainspring of a mechanical watch. Abraham-Louis Perrelet is credited as the inventor of the portable self-winding timepiece in the 18th century. The first series-produced automatic wristwatches date back to the Englishman, John Harwood, who patented a watch wound by a swinging weight in1923. In 1930 Rolex introduced a rotor-based winding system, in which the mainspring was wound in one direction of rotation. At the same time a range of other "jiggle-action" devices appeared, in which the movement itself acted as the oscillating weight, moving back and forth inside or with the case to wind the spring in both directions of motion. With the invention of the rotor mounted on ball-bearings by Eterna in 1948, all conditions were met for the future of self-winding systems. Automatic movements reached their production peak in the mid-seventies.

Baguette calibre A spiral hairspring attached at its inner end to the balance-staff and at its outer end to the balance-cock. The spring is three or four times thinner than a human hair and weighs around two milligrams, yet it can withstand a tension of 600 grams. Its elasticity enables the balance-wheel to swing equally back and forth. The active length of the spring determines not only the moment of inertia of the balance-wheel, but also the period of its oscillation. Lengthening the spring slows the balance; shortening it makes the balance go faster.

Balance-cock The bridge which supports the balance-wheel

Balance-spring A coiled hair-spring attached to the balance-cock and the balance-wheel. Together with the balance-wheel it constitutes the regulating organ of a movement.

Balance-spring stud A small metal fastening securing the outer end of the balance-spring to the balance-cock. The spring is either pinned up to the stud or, in modern watches, glued on.

Balance-wheel (see compensation balance) A wheel vibrating on a spiral balance-spring with which it forms the regulating organ of a mechanical watch. These two components are decisive in the precision of a watch.

Bars and cocks (see bridges)

Base plate A metal plate drilled with recesses and holes to take the wheels of the train and their pivots. The bars and bridges of the movement are also screwed onto the rim of the base plate. The under-dial work which drives the hands and other indications on the dial is mounted underneath the base plate on the dial side.

Bearing The holes in which the wheel-pivots turn. In the better watches and clocks jewel bearings are fitted, especially for the quickly revolving wheels and pinions. In simpler timepieces, the pivots turn in holes in the base plates, bars or bridges. Over time these can wear out, especially through lack of oil. Such bearings can be renewed by driving in a brass or bronze bushing.

Beat The number of vibrations of a regulating organ (pendulum or balance-wheel) in an hour. Two vibrations make a full oscillation

Bezel Strictly speaking, the rim holding the glass in a watchcase. The bezel fits onto the case band of the watch. Today, the word also denotes the various turning rings that are fitted on the faces of certain types of watch - the turning bezel in divers' watches, for example.

Bicolour cases  Cases  made with a combination of two metals.

Bimetallic balance (see compensation balance ) Bimetallic compensation balances were used in high grade watches before the invention of the self-compensating balance-spring. The rim of the balance wheel is cut in two places near its arm and made of two overlaid metals (steel and brass) with different coefficients of expansion. The moment of inertia of the balance-wheel thus changes with the temperature to compensate for the changing length or elasticity of a steel balance-spring.

Blind-man's wristwatch Special watches with hinged glass, heavy-duty under dial work, strengthened hands and hours in Braille so that the time can be told by touch.

Blued-steel hands and screws Bluing steel parts is an old craft tradition which requires experience and dexterity. The parts are roasted over heat in a small pan. At 300°C the surface briefly turns the desired blue, before changing colour again.

Bonding The process of incorporating integrated circuits in an electronic timepiece by soldering fine electric wires.

Bracelet Linked metal strap on a watch. The length can be changed by removing links.

Brass An alloy of copper ( 50 - 80 % ) and zinc ( 20 - 50 % ), and one of the most important metals used in watch making. The proportions of the alloy are chosen according to its application.

Breguet balance-spring 18th-century watchmakers experimented a great deal with balance-springs, trying out helical, conical and spherical springs to give the balance an isochronous oscillation. The decisive contribution to the improvement of the spring was made by Abraham-Louis Breguet, who saw that the outer terminal curve of the spring played the decisive role in making the spring develop concentrically and thus kept each oscillation of the balance of equal duration. After intensive studies he introduced the Breguet spring in 1795, characterized by its raised and shaped terminal curve.

Breguet hands This classic style of watch-hand can be easily identified by the hole near the tip. Also called moon hands.

Bridges Small metal parts holding the moving parts of a watch. Unlike bars and cocks, which have the same function, bridges are secured by screws to the base plate at both ends. They are named according to their role in the movement: centre-wheel bridge, barrel-bridge or balance-cock.

Broad arrow The pheon ( a bearing representing the head of a Broad Arrow or javelin, with long barbs which are engrailed on the inner edge ) was carried before royalty by a sergeant-at-arms. It became a royal mark, used in Great Britain to denote crown property, being termed the "Broad R," or "Broad Arrow." The Broad Arrow was chosen as the logo for the Military Watch Resource use as the official mark designating British Government issued property.

Brushed Steel  Stainless Steel with a Matt 'brushed' effect finish.

Buckle The buckle joins the strap together and is often made of the same material as the case of the watch.

Burnishing A polishing and cold-rolling process for pivots

Button A push piece on the case to control a function. Buttons are used to open a hunting-cased watch for example or to stop, start and zero chronographs. Some repeating watches were also controlled by a button instead of a slide.

Cabinotier (Fr.) An independent, and usually prosperous, watchmaker and owner of a workshop, typical of Geneva during the l8th and l9th centuries. Cabinotiers were the mainstay of La Fabrique Genevoise - the Geneva Factory - which made the city the capital of watch making.

Cabochon A spherical or domed cut given to gemstones. Cabochon stones are often set into the crowns of watches.

Calatrava An ornate cross belonging to an ancient Spanish order of knighthood. Adopted as a symbol by the Patek Philippe watch company.

Calibre Designates the size and/or construction of a movement so that it can be precisely identified, when ordering parts for example. Until the 1970s, a major movement-manufacturer could have more than 100 different calibres in production. Today this variety no longer exists. Traditionally, one distinguished between calibres for open-faced or Lepine watches (with the winding stem at 12 o'clock), calibres for hunting-cased watches (winding at 3 o'clock) and the various form calibres (baguette, tonneau, oval or rectangular).

Cambered Curved or domed glasses and dials are often found in old wristwatches. Occasionally the hands had a cambered surface as well.

Centre-seconds A seconds-hand mounted in the centre of the dial and reaching out to its edge.

CET Central European Time. On 1 April 1893, Germany and other central-European countries adopted the CET standard. CET is one hour ahead of the universal mean time based on the Greenwich 0° meridian (GMT).

Chablon (Fr.) A watch kit, or kit of watch-parts ready for assembly.

Chamfering The decoration of bridges, bars or steel-work in finely made movements by breaking the sharp angles of the components. The polished, angled edges eliminate metal particles that could fall into the movement.

Chaton (Fr.), bushing A metal ring holding a jewel-bearing. Chatons are riveted or screwed into plates, bridges and bars. Their original purpose was mainly aesthetic. Made of gold or other yellow metal they enhanced the brilliance and colour of the jewel. But watchmakers also found they had practical uses. Industrially produced chatons made the replacement of cracked jewels relatively easy. Inserting them took less work than setting a jewel. With the automation of movement manufacture, chatons grew in watchmakers' esteem. Holes to the exact size of standard chatons could be punched into the base plate. Chatons only become superfluous when manufacturers make consistently perfect jewels to exact standard sizes.

Chronograph A watch with conventional hours and minutes having additional mechanisms controlled by buttons to start, stop and return to zero a seconds-hand usually mounted in the centre of the dial. Most chronographs are also fitted with registers recording the elapsed minutes and sometimes the hours as well. When the zeroing button is pressed, the chronograph seconds-hand as well as the registers return to zero. (The etymologically correct term is "chronoscope").

Chronometer A very precise mechanical timepiece that has been issued with a rating certificate by an observatory. Modern chronometers are certified by Switzerland's COSC laboratory which conducts 16-day tests of the watches in five positions (crown left, crown up, crown down, dial up, dial down) and at two temperatures, 23.8° and 38°C. Wristwatches of a diameter greater than 20mm must meet performance standards in seven criteria.

Clock-watch A watch with a mechanism which strikes the time in passing, unlike a repeater which strikes the time on demand. Clock-work appeared in pocket-watches in the middle of the last century, chiming the hours and the quarters at each quarter (grand strike), or the quarters alone and the hour on the hour (small strike). Clock-watches often had a minute-repeater as well, striking the hours, quarters and minutes on demand. Wrist clock-watches have been in existence for around a decade.

Cloisonne (Fr.), enamel A design or picture drawn in partitions of metal which are filled in with enamel. The partitions, made of a ribbon of gold about 0.007mm thick and 1 mm high, prevent the different enamels flowing together. The cloisonne technique is sometimes used to decorate dials.

Club-toothed lever escapement Another name for the Swiss lever escapement, after the shape of the teeth on the escape-wheel. They are designed so that the lift is shared between the faces of the escape-teeth and the pallet-stones.

Coin silver An alloy of 90 % or 900 /1000 parts of fine silver and 10 % or 100 /1000 base metal

Cold-tempering Treating a metal by hammering and rolling when cold to achieve strength, density and elasticity.

Collet Split, cylindrical sleeve fitted to the balance-shaft, to which the inner end of the balance-spring is fastened.

Column-wheel chronograph Starting, stopping and zeroing a chronograph independently of the movement would not be possible without an intelligent control mechanism. Two different systems are used today. In the classic construction the chronograph functions are governed by a ratchet-wheel on which are mounted between five and nine vertical columns. Pressing the chronograph buttons advances the column-wheel clockwise through a specific arc. The columns act on sprung levers, which either rise on a column or fall between two, to initiate the appropriate function - start, stop or zero. Chronograph movements can be identified by the layout of their steel-work: levers, springs, wheels and column-wheel. Column-wheel mechanisms require a high level of finish, which has led manufacturers to devise low-cost alternatives. In these, the role of the column-wheel is assumed by swivelling, profiled cams.

Compensation balance (see bimetallic balance) Changes in temperature can have a negative effect on mechanical watches because they alter the elasticity of the steel balance-spring. A higher temperature causes the balance to lose rate; conversely lower temperatures make the watch gain. Eliminating the effects of temperature has been a major goal of chronometer-makers through the ages. More than 200 years ago the English watchmaker, John Arnold, invented the cut, bimetallic compensation balance that could counter the considerable effects of temperature on the steel springs of the time. The rim of the balance wheel is made of two metals brass overlaid on steel. As the temperature rises, the brass outer rim, which has a higher coefficient of 
expansion than steel, expands to force the cut ends of the rim inwards, reducing the effective radius of the balance and thus speeding it up to compensate for the lengthening of the spring. When the temperature falls, the rim opens and the balance slows. Because of the costs and skills involved in their manufacture, compensating balances are only used in the better watches.

Compilation Creating a new watch from mainly genuine parts from other watches. A good compilation - (a marriage) - is difficult to spot, and considerably reduces the value of a watch.

Complication A multi-part mechanism providing an additional horological function. Complications include repeater and chronograph mechanisms

Comptoir (Fr.) A watch dealership typical of the Jura region in the 19th century. The comptoir coordinated the production of watches by numerous craftsmen working from home and ensured the distribution and export of the completed watches.

Construction The conception and design of a movement, leading to a working prototype.

COSC Controle Officiel Suisse des Chronometres (Official Swiss chronometer-testing bureau). Founded in 1973.

Cosmograph As with a Chronograph, except that the Tachymeter function is found on the bezel of the watch.

Crown A button for winding the watch and setting the time and date. In earlier times, chronographs were also controlled through the crown.

Crown winding Until late into the 19th century, most pocket-watches were wound and set with a small key. In modern watches, a crown with a switching mechanism performs one or other of these functions.

Crystal The glass on a watch can be made of Plexi Glass (A synthetic Crystal) or Sapphire Crystal depending upon its make and age. Cylinder escapement A watch escapement invented by the English watchmaker George Graham in 1726. The teeth of the escape-wheel engage an opening in a hollow cylinder mounted on the balance-staff, instead of a pallet-lever. In wristwatches it is limited to earlier or cheaper models. Its unsatisfactory performance, compared to the lever escapement, has now consigned the cylinder to history.

Date indications The date is shown either by a hand (analogue date) or by an under dial ring, revealing the date through a window in the dial (digital date). Both complete one revolution in 31 days, advancing to the next day at around midnight. Date-changes can be progressive, taking place over a period of an hour or two, or instantaneous.
Deployment Buckle The clasp folds under the strap of the watch.
Detent escapement A delicate and precise escapement used for chronometers. The stone that locks and unlocks the escape-wheel is carried on a sprung or pivoted blade (the detent), and the impulse is given by the escape wheel as it flicks past a jewel on the impulse roller of the balance.

Digital indications The time shown in figures without a hand. Digital hours, minutes, seconds and dates predate the quartz watch. Wristwatches with digital indications appeared shortly after 1910. In mechanical watches digital indications are given by rotating disks or rings.

Double chronograph Strictly speaking a pocket-watch with two independent chronograph mechanisms. Such watches have been made by Audemars Piguet, Patek Philippe and A. Lange & Sohne. Double chronographs have yet to appear in wristwatches, where the term generally means a split-seconds chronograph.

Double-sided watch A watch with two back-to-back dials. In the 1930s, Mimo's double-sided "Mimorex" ladies' watch showed analogue and digital time on its two faces.
Duo-dial/Doctors watch An early wristwatch featuring two dials; hours and minutes, and a lower seconds dial. For example, a Rolex Prince.

Dust-cover A second cover over the case-back of a watch. It was a feature of pocket-watches which had key-holes in the case-back, which would let in dust. Occasionally wristwatch cases have also been made with a dust-cover.

Ebauche (Fr.) The movement-blank comprising the main structural parts of the movement: the base plate, bars and bridges, set of wheels and steel parts. Not included are the power source (main spring), regulating organs (balance and escapement) and the indicators (dial and hands). Today ebauches can also be provided fully jewelled.

Eight-day movement A mechanical watch or clock movement that only needs to be wound once a week. There are a number of known constructions for wristwatch movements, including the "Hebdomas" launched in around 1913, in which the mainspring barrel covers the whole surface of the movement. Rectangular models from the thirties mostly had form movements with a standard-sized barrel and a geared-down going-train with intermediary wheels.

Elapsed-time register A watch that can measure and register short periods. For example stopwatches and chronographs.

Electric timepieces These include models with electric winding, or with electronically governed balance-wheel or pendulum. The development of electro-mechanical wristwatches dates from the early fifties.

Electronic timepieces Clock and watches with solid-state (transistorized) control of the power supply.

Enamel (see cloisonne) Coloured glass fused over metal, as protection or decoration. In the 19th and early 20th centuries, enamel dials were virtually standard for high-grade watches. Due to the cost, they have almost completely disappeared from the market over the past decades.

End-stone A watch jewel without a hole. The end-stone is placed over a pierced jewel to limit the vertical movement of the wheel pivot. End-stones are used to cap the balance-staff and, in expensive watches, are also used for the pivots of the escape-wheel and pallet lever.
Engine-turning, guilloche (Fr.) The mechanical engraving of fine and intricate patterns on watch-cases or dials.

Equation of time Because of Earth's elliptical orbit and inclined plane the difference between the longest and shortest solar day of the year amounts to 30 minutes and 45 seconds. The constantly changing length of the solar day means that using true solar time would bring intractable problems to daily life. For this reason mean (average) solar day was defined consisting of 86,400 seconds - the average length of the true solar days of the year. Mean solar time, or civil time, is that indicated by ordinary clocks and watches. The equation-of-time indication, which has become increasingly rare since it was invented in the late 17th century, shows the difference between mean time and solar time. The greatest differences occur in mid-February (+14min., 24sec.) and early November (-16min. 21sec.). Four times a year, on 16 April, 14 June, 1 September and 25 December, the lengths of the true solar day and the mean solar day are identical. The equation-of-time indicator, either a second minute hand or a hand on a separate scale, works off a kidney-shaped cam that goes round once a year. The cam's profile is cut to represent the changing difference between mean and solar times. Breguet are among the rare makers of wristwatches with equation-of-time indication.

Escape-wheel A specially toothed wheel engaged by the pallets of the lever

Escapement A mechanical device that delivers the energy of the mainspring in small impulses to the balance-wheel, at the same time preventing the mainspring unwinding rapidly. In a watch with a balance frequency of 28,800 v/h, the locking and unlocking of the escapement advances the wheel-train 691,200 times a day.

Fast-beat movement Movements in which the beat of the balance is increased to give greater accuracy and to reduce sensitivity to shock. Their balances vibrate at 21,600, 28,800 or even 36,000 times an hour.

Fine gold 24 karat or 1000 / 1000 gold
Fine silver A metallic element commercially pure .999 /1000

Finishing The detailed workmanship that goes into improving the appearance and function of a watch.

Flat balance-spring (see balance-spring) These include models with electric winding, or with electronically governed balance-wheel or pendulum. The development of electro-mechanical wristwatches dates from the early fifties.

Fly-back hand In a retrograde indication, the hand that reaches the end of a scale and automatically flies back again to the beginning. In chronographs, the hands that can be made to return to zero.
Form movement Any watch movement that is not round. Shapes include tonneau, baguette, rectangular, square and oval. Today form movements are an exception.

Frequency Oscillations per unit of time, measured in hertz (Hz). In clocks, the frequency is regulated by the pendulum, and in watches by the balance, both vibrating at a set rate.

Full calendar Showing the day, date, month and sometimes also the phases of the moon.

Geneva seal The Geneva Seal hallmark was instituted by the Geneva legislation of 6 December 1886 on the voluntary inspection of watches. It established the conditions to be met in the manufacture of watch movements. In 1975, the rules were updated, setting 11 conditions to qualify for the hallmark, including the timekeeping performance of the watch. Wristwatches of less than 30mm diameter were subjected to an 18-day rating test. The Geneva Seal rules were last revised on 22 December 1994. Watches submitted to the "office for the voluntary testing of Geneva watches" for the coveted hallmark must have numbered movements. Most of the conditions, expressed in 12 articles, concern the quality of finish and workmanship in the various movement components. The Geneva Seal demands that the movement must be finished and assembled in Geneva.

Geneva stripes Bars and bridges of a movement before rhodium-plating. Used in high-grade watches.

Glucydur balance The modern balance-wheel that superseded the bimetallic compensation-balance with the advent of the compensating spring. Glucydur balances are made of copper alloyed with 3 % beryllium and 0.5 % nickel, and can be recognized by their gold colour. Ordinary nickel balance-wheels have a silver colour. Glucydur has a hardness of 380 Vickers against 220 for nickel and 180 for brass, ideal for riveting, poising and adjusting the balance-wheel.
GMT Greenwich Mean Time, or Universal Time (UT) at the Greenwich meridian. GMT is today's standard time for navigation and international radio.

Going-train The assembly of wheels and pinions which transmits power from the mainspring barrel to the escape-wheel

Gold alloy A metal composed of two or more elements, one of which is fine gold. The alloy is obtained by fusing a mixture of metals.

Gold electro-plate At least 7 millionths of an inch of fine gold required electro-deposits in an article marked gold electro-plate

Gold plating Electronic deposit of a coating of gold, on watch-cases made of base metal, for example.

Gold-filled A layer permanently bonded by heat and pressure to one or more surfaces of a supporting metal, thence rolled or drawn to a prescribed thickness. The karat gold layer must be at least 1/20th by weight of the total metal content.
In order to mark a watch case gold-filled, the gold layer must be 10 karat or better and must be at least three thousandths of an inch thick.

Gold-plate An optional term to describe a gold-filled or rolled gold plate product

Grand complication A highly-complicated pocket- or wristwatch, combining at least chronograph, repeating and perpetual-calendar functions.

Gravity (see tourbillon) The influence of gravity on the rate of mechanical watches should not be underestimated, especially in pocket-watches which are worn upright. The force of gravity can significantly disturb the rate of the watch if the centre of gravity of the balance-wheel and its physical centre do not coincide. This unbalance means that there will always be a part of the balance-wheel's rim that will seek the lowest point, causing the balance to speed up or slow down.

Guilloche A type of Dial. As opposed to a flat colour, a Guilloche dial is textured with engravings.

Gyromax balance On 31 December 1951 Patek Philippe patented its Gyromax balance. Set on vertical pins around its edge were eight split weights that could be turned to adjust the balance. Initially Patek Philippe also fitted the usual fast/slow precision-index to adjust the rate of the balance. But the adjustment possibilities of the Gyromax come into their own when it is free-sprung - without an index. For that reason, Gyromax balances are today always free-sprung, even when used by other watch makers.

Hack(ing) feature HACK is military slang for synchronizing several timepieces to a single time source. ( see also „stop-seconds„ )

Half-hunter Watch with a sprung cover over the dial. The cover has a usually circular window in the middle to reveal the time without having to open it. Half-hunter cases are mainly used for pocket-watches, but in the 1920s when watch-glasses were easily and often broken, half-hunter wristwatches were also produced. Unlike the pocket half-hunters, the opening in the dial-covers of wristwatches generally had no glass.

Hallmarks and maker's marks Hallmarks punched into the case certify the fineness and the provenance of precious metal. Maker's marks can also be found stamped on the case or movement.

Heavy gold electro-plate At least 100 millionths of an inch of fine gold required electro-deposits in an article marked heavy gold electro-plate
.
Hectometre scale A chronograph scale to determine the flow of liquids.

Helium Escape Valve Decompression System allowing helium to escape from inside the watch. Used professionally in decompression chambers.

Horology The art and study of clock and watch making.

Hour-register A feature on many chronographs which counts the hours elapsed since the chronograph was started. Most hour-registers go up to 12 hours, with the hand jumping forward one hour each time the minute-register completes a revolution. The hour-register is returned to zero with the other chronograph indications.

Hunting-cased watch/hunter A pocket-watch case with a sprung cover hinged over its glass. The winding stem or pendant are usually at 3 o'clock on the dial.

Incabloc One of the most widely used shock-proofing systems for mechanical watches, in series production since 1933. in 1938 an improved version came out, and Incabloc has since proved itself the most successful method of shock-proofing in watch making history, not least because it is easily fitted to all calibres.

Incastar A system to adjust the rate of a watch without the normal fast/slow index, developed by Portescap. The outside end of the balance-spring spiral is held between two sprung rollers. A small star (hence the name) on one of the rollers allows the rate of the balance to be changed by lengthening or shortening the spring.

Index Component enabling the daily rate of the watch to be adjusted fast or slow.
Index mobile A relatively simple and cheap, yet effective construction for a chronograph with a split-seconds hand, first patented in 1948. As in the conventional split-seconds chronograph, a second arbour goes through the cannon of the chronograph hand. This arbour has a stud at its end. The two hands are connected by a coiled hairspring, the chronograph-hand carrying the split-seconds hand with it. A pin under the chronograph-hand prevents the split-seconds hand overtaking it. A button in the crown controls a brake that acts on the stud, stopping the split-seconds hand (to take an intermediary time), while the chronograph-hand keeps running. Releasing the button allows the spring to bring the two hands together. The maximum interval for intermediary times is 60 seconds, because the pin on the running chronograph-hand comes up against the stationary split seconds hand after one minute.

Indirect centre-seconds Movements in which the drive for the seconds hand is outside the going-train. Indirect centre-seconds are most often found in calibres for small-seconds that have been converted into centre-seconds movements to follow prevailing fashion. Modern centre-seconds watches have purpose built calibres in which the seconds are usually driven directly from the going-train.

Integrated circuit An electronic chip incorporating several thousand transistors. In a quartz watch, it maintains the vibration of the quartz, divides its frequency and controls motor functions.

Isochronous Occurring in equal periods of time. Each oscillation of the balance-wheel must be of equal duration to achieve perfect isochronisms.

Jewel Corundum stone (usually synthetic ruby) used as a low-friction bearing. Pivot-jewels are drilled and olive-cut, or un-drilled end stones. Pallet-stones in the lever engage the escape wheel.

Jewel bearing A cylindrical, pierced stone, today usually made from synthetic ruby. Jewels, set into holes in the base plate, bars and bridges, hold the pivots of the faster wheels of the movement. The better watches have donut-shaped jewels where the inside of the hole is rounded to reduce the contact with the pivot to the minimum. These "olived" jewels also eliminate any play in the pivot.

Jewels (see rubies) The international term for the bearings and parts made of synthetic or real gemstones in a watch. In precision watches, jewels are used to reduce friction in the main bearings (pierced jewels and end-stones), the pallet-lever (pallet-stones) and the roller (impulse pin). In earlier times natural ruby or sapphire was used, but today the stones are entirely synthetic. A large number of jewels advertised on the dial does not necessarily mean a better watch. Often these jewels are not placed where they are meant to be. A manually wound precision watch needs at least 15 functional stones: 10 jewel bearings, two end stones for the balance-staff, two pallet-stones for the lever and one impulse pin. The optimum number of jewels is 18.

Jig borer Measuring and machining instrument, which positions the work according to co-ordinates set in a rectangular frame.

Jump hours A watch movement that replaces the hands on the dial with a disk bearing the 12 hours. An additional mechanism makes the disk jump forward 30° of arc every 60 minutes, revealing the next hour through an aperture in the dial. Jump hour wristwatches were popular in the twenties because they gave the dial a new look. Pioneers of this type of indication included Audemars Piguet, C. H. Meylan and Patek Philippe. Also from that time are "digital" watches in metal cases with small apertures in the dial for hours, minutes and seconds. One of the most popular jumping-hour models of the thirties was the Rolex "Prince". The sixties saw the production of a variety of wristwatches with jump hours.

Jumping seconds Defined in a patent application as "a device for the step-by-step advance of the seconds-hand driven by the movement." In an ordinary movement, beating at 18,000 v/h or five times a second, a small additional escapement releases the seconds-hand after every five vibrations, allowing it to jump forward second-by-second, like the seconds-hand of a quartz watch.

Karat Refers to the amount of gold in an alloy. 24 k is pure, 18 k contains 18 parts of gold in 24 parts of metal, thus 18 k is 18/24 or 75 % or 750 o/oo gold. Similarly 14 k is 58.3 % gold and 10 k is 41.6 % gold.

Kit (see chablon) A set of all the parts for the assembly of a watch.

Lapping Shaping metal by grinding and polishing it to exact dimensions. Lapped edges and surfaces add considerably to the appearance of metal parts, notably applied hour-markers on the dial.

LCD Liquid Crystal Display. Liquid-crystal films, which scatter light in an electric field, have assumed enormous importance, notably in digital quartz watches.

Leap-year Every fourth year in the old Julian calendar had 366 days (with the addition of February 29), to adjust for the difference between the calendar year and the year of the sun's orbit. In the Gregorian calendar, which we use today, the regular four-year cycle is broken three times every four hundred years. In the secular years indivisible by 400 (2100, 2200, 2300, 2500, 2600) the expected leap-year does not occur.

Lepine calibre Movements in which the wheel-bearings are held by several bridges instead of a single large plate.

Lever Anchor-shaped part of a watch escapement usually made of steel or brass and holding the pallets that engage the escape-wheel.

Lever escapement The most widely used type of escapement for watches, invented the 1800s. There are several varieties of this escapement with its characteristic anchor shaped pallet-lever: The English pointed-tooth escapement; the German Glashutte lever; the Swiss club-toothed escapement and the pin-pallet escapement.

Ligne (Fr.) An old unit of measurement in watch making, derived from the Pied du Roy, the French "royal foot," and equal to 2.2558 mm. Dimensions of watch-movements are still expressed in lignes ("'): e.g. an 11-ligne round calibre, or a 8'''x 12"' form movement.

Lugs On the case, this is where the bracelet or strap is joined.

Luminous dial A dial on which the time can be read in the dark. The hands and hour-markers are coated with a luminous substance. Earlier, radium was used; today this has been replaced by tritium, mesothorium or radiothorium. Phosphorescent salts are also used, notably zinc sulphide. The German physicist, Philip Lenard (1862-1947) conducted intensive research to identify more that 1000 luminous substances (silicates, sulphides or wolframate), which glow in various colours.

Maillechort German Silver : an alloy of copper (50-80 %), zinc ( 20-30%) and nickel (10-20%)

Mainspring barrel A flat cylindrical drum mounted on a large toothed wheel, turning around a central arbour. The mainspring, coiled inside, turns the drum and its wheel. The teeth of the wheel engage the first pinion of the wheel-train, supplying power to the escapement.

Maker's mark (see hallmark) A usually easily-identified symbol on dials and engraved or stamped on movements and cases.

Manufacture (Fr.)  A watch factory. According to an unwritten watch making law, a watch company is only entitled to call itself a manufacture if it manufactures at least one calibre of its own construction. For example; Audemars Piguet, Chopard, Citizen, Corum, Girard-Perregaux, Glashuetter Uhrenbetrieb, IWC, Jaeger-LeCoultre, A. Lange & Sohne, Patek Philippe, Piaget, Rolex, Seiko, and Zenith.

Mechanical clock A clock driven by weights or a spring and regulated by a swinging beam or pendulum. The first all mechanical clocks were developed in the late 13th century. One of the oldest mechanical clocks in continental Europe is that of Strasbourg cathedral.

Megahertz (MHz) A frequency of one million oscillations a second.

Military or 24-hour time When time is measured in 24-hour segments. To convert 12-hour time into 24-hour time, simply add 12 to any p.m. time. To convert 24-hour time into 12-hour time, subtract 12 from any time from 13 to 24.

Milling machine A machine tool with hardened cutting edges for a wide range of metal work. 

Mineral glass Watch glass that has been tempered to increase its scratch resistance.

Mini-rotor A small winding rotor sunk into the base plate of the movement of some automatic wristwatches.

Minute repeater A timepiece that can be made to strike the time in hours, quarters and minutes, by means of a push-piece or slide.

Minute-register An indication on stopwatches and chronographs that counts the elapsed minutes. Most registers go up to 30 or 45 minutes, but 15- and 60-minute registers also exist. The hand registering the minutes flies back to the beginning of its scale when the chronograph (or stopwatch) is zeroed.

Modular complications Complicated watches in which the additional mechanisms for the chronograph, repeater or calendar are mounted on separate plates that can be fitted on to a movement. Modules, which can be constructed to adapt to existing movements, are a cost-effective solution and are used in most complicated timepieces. Integrated complications such as repeaters and chronographs are purpose-built and designed as a whole.

Module A mechanical entity. The chronograph mechanisms in many modern chronographs are mounted as modules under the dial, usually driven from the movement by a friction-wheel. Modular constructions are also used for perpetual-calendars, in which the calendar work, comprising around 60 parts, is mounted on its own plate under the dial.

Moon-phase The lunation - the period from one new moon to the next - is exactly 29 days, 12 hours, 44 minutes and 3 seconds. The phases of the moon are shown by a disk with 59 teeth around its edge and two moons depicted on its surface, facing one another. The moons-disk, driven by the movement, completes one rotation every 59 days, or in two lunations. The two moons succeed one another to show their phases through a semicircular aperture with curved lunar terminators cut into the dial. Some moon-phase indicators have a scale of 29 1/2 days to show the age of the moon.

Movement The fully functioning assembly of all the main timekeeping organs of a watch.

Mystery clock or watch A transparent clock which appears to have no mechanism.

Noon The basis of all time reckoning is the apparent movement of the sun across the sky. True noon is when the sun crosses the observer's meridian, throwing the shortest shadow.

Olive cut Describing the slightly convex cut in the inner circumference of a jewel bearing.

Oscillating weight (see rotor) The pivoted weight in an automatic movement connected through a winding-train to the mainspring. Unless the watch is perfectly flat, gravity attracts the weight to the earth's centre. The motions of the wrist provide the kinetic energy which is stored as potential energy in the mainspring barrel.

Overlay An acceptable terminology of gold-filled - the quality requirement is the same as for gold-filled.

Oyster Invented in 1926 by Rolex. At the time it was described as" the first  waterproof, airtight and dustproof watch. Named Oyster due to its shape.

Pallet-lever One of the most complex parts of a mechanical watch. The lever, made of brass or steel, is fitted with the pallet-staff, pallet stones and the guard pin. Its role is to transmit power from the going-train to the balance, and to maintain its oscillations. The pallet-lever at the same time works with the escape-wheel and balance to release the energy transmitted by the going-train in isochronous increments.

Parachute The name Abraham-Louis Breguet (1747-1823) gave to the anti-shock device he invented for his watches. To prevent the balance-shaft breaking if the watch should be dropped or knocked, he devised a sprung jewel bearing to absorb the shock.

Parts These include finished springs, winding shafts, pinions, wheels etc. as parts for production or replacement.

Pedometer-wind A weight mounted on a sprung pivoting arm that swings up and down to wind the mainspring of a watch through a ratchet-train. In this way automatic pocket-watches are wound while the wearer is walking. Abraham-Louis Perrelet of Le Locle is credited with inventing this device in 1770. The first adaptation of the principle to wristwatches came in the 1920s (Leon Leroy in 1922 and John Harwood in 1924), with the weighted winding-arm swinging through a much greater arc. These non-rotary self-winding systems were in use until the 1950s.

Perpetual calendar A complicated calendar mechanism comprising some 100 parts which takes account of months of different lengths and needs no manual correction. The mechanism is usually mounted on its own plate under the dial. The months of different lengths are determined by the months cam, with recesses cut at corresponding positions around its edge. Perpetual calendars, which usually indicate the days, dates, months, moon-phases and leap-year cycle, are programmed to operate automatically until 28 February 2100, when the normal four-year leap-year cycle is next broken. The smallest perpetual-calendar movements to date have a diameter of 23mm.

Pillar-plate watch The construction of the earliest watch movements was between two plates supported by carved pillars. It survived, with plain cylindrical pillars, as the construction of the cheapest watches.

Pin-pallet escapement (see roskopf watch) The pin-pallet escapement for clocks was invented by Amant in the mid-18th century. In watches, it goes back to Georg Friedrich Roskopf in 1867. Roskopf wanted to make accurate watches available to the poorer sections of the population. He therefore developed a simple movement, devoid of luxurious refinement, that could be cheaply made. Roskopf recognized the shortcomings of the widespread cylinder escapement, but he did not want to dispense with the proven advantages of the lever escapement. To cut costs, he replaced the pallet-stones of the lever with upright pins that engaged I the teeth of the escape-wheel. Hence the name pin-pallet escapement.

Pinion Part mounted on the shaft of a wheel, the leaves of which engage the teeth of a neighbouring wheel.
Pink Gold (Also Rose Gold) Gold metal with a pink/rose tint

Pivot-shank Part of a shaft, situated, for example, between the pivot and the pinion-leaves.

Plate A metal plate that supports the bridges and various parts of the movement.

Power-reserve The amount of energy maintained in a wristwatch if it is fully rewound once every 24 hours. In these conditions the power reserve usually fluctuates between 10 and 16 hours. A lower power reserve will affect the rate of the balance as the spring loses its energy.

Power-reserve indicator, up/down indicator Shows the remaining running time in a watch.

Power-supply In mechanical watches, the potential energy comes from a wound spring; in clocks, from raised weights; and in quartz watches from batteries, accumulators or condensers.

Precious metals Gold, platinum and silver. Gold, used to make wrist-watch cases, can be found in alloys of increasing fineness: 333/1ooo (8 karat), 375/1ooo (9k), 565/1ooo (14k) or 750/1ooo(18k). The colour of the gold (yellow, pink or white) is determined by the other metals in the alloy. High alloys of gold (21 k to 24k) are too soft for watch cases and are used for winding rotors in automatic movements. platinum is mostly 950/1ooo fine for use in cases and bracelets. Silver wrist-watch cases are rare and are invariably gold plated to prevent tarnishing.

Precision adjustment The art of eliminating or countering all the factors that can disturb the rate of a watch. The degree of adjustment is determined by the producer of the watch and ultimately by the price.

Precision index A device enabling a very fine adjustment to the rate of the watch by moving the fast/slow regulator in tiny increments. A variety of methods can be found in mechanical watches, from the exclusive swan's neck adjuster to the more popular "Triovis" type with adjusting screws. However, a precision index does not in itself mean higher precision. A watch with an ordinary regulator can also be adjusted exactly.

Precision watch A watch with a lever or chronometer-detent escapement, temperature compensation and assembled from the finest components. Precision watches should have at least 15 jewels.
Press A high-precision tool for punching, bending and cutting out many of the preliminary parts of a watch.

Production number A way of identifying watch cases and/or their movements. Many manufacturers number their watches in sequence with the lower numbers indicating earlier production dates. Others use different numbering systems, with a code for each calibre, enabling initiates to identify particular movements.

Pulsometer A chronograph, mainly for medical applications, with a scale that gives the pulse rate. The chronograph is made to run for 20 or 30 pulse-beats, according to the version, and the pulse rate per minute is read off the scale against the stopped chronograph hand.

Pump-winding An early form of keyless winding in pocket-watches by pushing and pulling a winding shaft in and out of the case

Quartz watch An electronic timepiece, with analogue or digital indications, regulated by a quartz crystal vibrating in an electric current. The standard frequency of modern quartz watches is 32,768 Hz.

Radio-controlled watches and clocks Timepieces with a receiver to pick up radio time signals; for example, the exact atomic time broadcast at a radius of 1500 km from the DCF 77 long-wave transmitter at in Mainflingen near Frankfurt/Main. The signals automatically synchronize the watch, when it is within range, while a quartz movement keeps it going.

Railroad watches Their dials often had two hour scales, 1 to 12 and 13 to 24, in distinct colours or styles. Until the 1930s, railway watches were large pocket-watches. Since then, railway staff have relied more on wristwatches. Special "railway" wristwatches have anti-magnetic inner cases because of the strong fields generated by electric locomotives.

Recess The housing machined out of the bottom plate, designed to accommodate wheels, pinions and other parts of the movement.

Reference The code in numbers and letters watch-producers use to identify each model. The reference code can also contain information about the type of watch, the material its case is made of, its movement, dial, hands, strap or bracelet and jewel settings.

Regulating organ In a mechanical watch, it's the balance-wheel and balance-spring working together to give a steady as possible rate to the movement.

Regulator dial A style of dial typical of regulator clocks, indicating hours, minutes and seconds separately. Its main characteristic is the decentralized hours, so that the hour hand does not obscure the all-important seconds indication. Regulators are the master clocks used in observatories and chronometry workshops.

Repairer's marks Watchmakers often leave their mark inside the case back of a watch after repair. Experts can determine the age and life history of a watch from the style, dates and numbers of repairer's marks.

Repassage (Fr.) The thorough re-examination or overhaul of a completed watch, including a verification of the rate, before it leaves the factory for sale. In earlier times the watchmakers performing this task were regarded as the elite.

Repeating work A horological complication that indicates the time more or less exactly by sound. Repeaters fall into different categories, striking the time on demand to the nearest quarter-hour, 1/8-hour (7 1/2 minutes), five minutes or minute. (These are known respectively as quarter repeaters, half-quarter repeaters, five-minute repeaters and minute-repeaters). Repeating work is powered by its own spring which is armed by pushing a slide or a button on the case. Releasing the slide also starts the strike. Simple repeaters will only give a partial strike of the time if the mechanism is not fully armed. In the more sophisticated "all-or-nothing" constructions, the strike will only be released if the slide or button is pushed home and the mechanism fully armed. The earliest repeating watches (quarter-repeaters) date from 1687, while minute-repeaters first appeared in around 1750. The first repeating wristwatch was probably made in 1892. The smallest movement with minute-repeater has a diameter of 13.53 mm.

Retrograde indications (see fly-back) Hands indicating the hour or date along an arc graduated 1 to 12 or 1 to 31. When it reaches the end of the scale, the hand flies back to the beginning.

Rhodium A hard, brittle, non-oxidizing metal in the platinum group.

Rhodium plating The electro-plating of the surfaces of a movement, to improve its appearance and to prevent tarnishing. Rhodium, which is a platinum-group metal, also gives the parts a harder surface.

Rolled gold plate Rolled gold or double cases are generally made of a base metal covered with a thin coating of precious metal, typically a few microns (millionths of a meter) thick. A 20-micron gold coating is just 2/2oo mm thick.

Rose gold (also pink gold) Gold metal with a pink tint due the higher presence of copper.

Roskopf watch A construction for a cheaply made movement that brought watch-ownership to everyman. Developed in 1867 by watchmaker Georg Friedrich Roskopf (1813-1889), these so-called "proletarian watches" were noted for their robust build and remarkable accuracy. Vertical pallet-pins instead of jewels engaged the teeth of the escape-wheel, while the movement was between two plates in a pillar-plate construction. Other features of the Roskopf movement included a light balance-wheel, a relatively thick and unbreakable balance pivot, a minimum of jewels (usually only four) and no finishing.

Rotor A pivoted weight revolving through 360° to wind the mainspring in automatic watches. In some constructions the rotor winds only in one direction of its rotation; in others it winds both ways through a reverser gear. Central rotors are mounted above the movement, while mini-rotors are set off-centre, flush with the surface of the movement.

Rubies (see jewels ) In around 1700, three foreigners living in London, the Swiss mathematician Nicholas Facio and the two Frenchmen, Peter and Jacob Debauire, recognized the value of pierced rubies as bearings in watches. In those days, the pivots of escape-wheel, pallet-lever, balance-staff and the wheels of the going-train turned in holes drilled into the brass base-plate and bridges. Pressure and the high velocity of the rotating pivots caused wear through friction. The use of pierced rubies as bearings gave English watch making an advantage over its continental rivals throughout the 18th century. The new jewel-bearings reduced friction and wear, significantly lengthening the life of a watch. Since 1902, artificial - or more properly, synthetic - rubies have been used in watch movements. Synthetic rubies are hard, homogeneous, relatively easy to work and come in a choice of colours. They superseded the reconstituted rubies, made from ruby debris heated under pressure, and not noted for their quality. The cost of real ruby gemstones virtually prohibits their use in watch-movements. Synthetic rubies have identical properties to those of natural rubies, and differ only in the way they are created. The low-cost mass production of synthetic rubies during this century has made them available to an increasing number of relatively cheap watches. Functional jewels in a watch are a sign of its quality and an argument for its sale.

Running time The time a mechanical watch will run from a fully wound state until the spring is exhausted and all movement ceases.

Satin finishing Imparting a silky, matt finish to metal surfaces.

Second The duration of the secunda minuta - the second subdivision of the hour - has had to be redefined several times over the years, not least because of the enormous progress made in the measurement of time. In 1820 a French scientific committee proposed that a second should be one 86,400th part of a mean solar day. Evident irregularities in the rotation of the earth, and modern quartz-based time-measurement made a new definition necessary in 1956. The new duration of a second equalled one 31,556,925.9747th part of the Earth's orbital years beginning on 1 January 1900. However, this cumbersome definition was not to last. It was far too imprecise, accumulating an error of around five seconds in 1000 years. By the end of the fifties, quartz clocks were showing themselves inadequate as atomic clocks took over the measurement of time. Since 1967 a second has equalled the time taken by 9,192,631,770 periods of radiation in the transition of a caesium isotope.

Seconds indication The seconds-hand is said to have been introduced by Jobst Burgi in around 1579, and was originally intended for the most precise timepieces. Today it is seen in all types of watches.

Self-compensating balance-spring Introduced in the early thirties, balance-spring made of special alloys averaged out the effects of temperature changes and other disturbances on the rate of the watch.

Self-winding (see automatic winding)
Semi-perpetual calendar A calendar watch that automatically adjusts for months of different lengths except for February in a leap-year. To account for 29 February as well, it would need a wheel that makes one revolution every four years. Wristwatches with a semi-perpetual calendar are rare and also not much in demand, for their price advantage over a fully perpetual calendar is slight.

Servicing A mechanical watch performs heavy work, and should be cleaned and oiled at least every four years. Regular servicing is taken for granted for automobiles which, on average, run only a few hours a day. A watch runs 24 hours a day, while foreign particles and the decreasing viscosity of the oil lead to increased friction. This can damage the pivots of the wheel-train. Ideally a watch should be completely overhauled and thoroughly checked at each service.

Screw-Locking Crown (Also Screw-in Crown) The screw-in crown seals the crown against the case and aids water resistance.

Shock-protection (see incabloc and parachute) A system to safeguard the fragile pivots of the balance-staff. The jewel bearings and end stones of the pivots are mounted on springs in the balance-cock and the base plate, so that they can absorb shocks both laterally and along their axis. By definition a shock-resistant wristwatch must be able to withstand being dropped from one meter onto an oak floor, without showing any deterioration of rate. The earliest shock-protected wristwatches date from the 1930s, and shock-resistant devices have been standard in mechanical wristwatches since the fifties.

Shuttle chronograph In this chronograph construction, the start, stop and zeroing functions of the chronograph are programmed into a cam that can be shifted from one position to another. Although technically less sophisticated than the column-wheel construction, the shuttle is no less reliable.

Sink A highly polished concave chamfer around a hole in the hub of a wheel.

Six positions In rating a watch, its time-keeping performance is observed in six positions.

Skeleton work A movement in which all the components - plates, bridges, bars, barrel-cover and rotor - are cut away to make them as transparent as possible. Only the most essential structure of the part is left. In the best watches, the open-work is all done by hand, in simpler watches skeleton movements are made by machine. Skeleton wristwatches date from the mid-1930s. 

Split-seconds chronograph A chronograph with two seconds-hands which rotate together. One of the hands - the split-seconds hand - can be stopped independently to record an intermediate time, and then be made to catch up and run together with the other hand. Both hands can be stopped and zeroed together. Split-seconds chronographs are used to time individual participants in a race, for example. Because of the high cost of the complex split-seconds mechanism, such chronographs are rare and typically 50 percent more expensive than ordinary chronographs.

Spring bar The thin rods with sprung, telescopic ends, securing a watch band to the case between its two lugs, or horns. The sprung ends enter corresponding holes in the inside of the lugs.

Springs (see balance-spring and mainspring) The spiral hair-spring of a watch balance needs around one trillionth of a horsepower to maintain the oscillations of the balance-wheel. This power is delivered through a train of wheels by the mainspring, and lasts barely two days, depending on the type of movement. The mainspring is contained in the mainspring barrel - a circular drum. The outside end of the spring is hooked on the inside band of the barrel, while the inner end of the spring is fastened to the barrel arbour. Mainsprings made of ordinary steel are now a thing of the past. Since around 1945, a succession of special steels have been coiled inside mainspring barrels. Such springs, of which "Nivaflex" is a major example, have a number of real advantages: they neither break nor rust and resist distortion. Moreover they are virtually anti-magnetic, and their life span, if properly handled, is remarkably long. Theoretically a mainspring from a used watch can be fitted into another watch of the same calibre without any problem.

Stainless steel The nickel and chrome steel used in watches can also contain tungsten or molybdenum. It is extremely hardwearing, resistant to corrosion, anti-magnetic, but also difficult to work with.

Staybrite A commercial term denoting the rust-free qualities of stainless steel and sometimes found stamped on the case back.

Sterling silver  An alloy of 92,5 % (925)  parts of fine silver and 7,5 % (75) base metal or other suitable alloys.

Stone (see jewel)

Stop-seconds A mechanism to stop the movement so that it can be set precisely to the second, from a time signal, for example.

Stopwork A device in the shape of a Maltese Cross to ensure an even power-supply from the mainspring barrel. It works with a finger on the barrel arbour to compensate for the biggest power variations from the spring. This sophisticated technique is now only used in the finest watches.

Subsidiary seconds An off-centre seconds indication, usually at 6 o'clock on the dial. In some chronographs the small-seconds are placed at 9 o'clock.

Swan neck regulation This gives a greater accuracy to the performance of a watch, used particularly in chronometers.

Sweep-seconds A Hand that makes a complete sweep around the watch face during one minute, to indicate the passing of seconds.

Swiss lever escapement  A detached escapement for watches characterized by the club-shaped teeth of the escape-wheel. The lift of the pallet-lever is shared between the ruby pallet stones and the escape-teeth. Two other versions of the lever escapement are the English lever and Glashutte lever.

Swiss made In today's hotly-contested watch market, countless watches are entitled to put Swiss Made on the dial without actually deserving the title. They are taking advantage of a revision of the ordinance decreeing that a watch is Swiss Made if a Swiss movement has been cased-up and checked in Switzerland. A movement is regarded as Swiss if at least 50% of its parts by value (not counting assembly costs) have been manufactured in Switzerland. Thus a Swiss Made watch need only have its dial, hands and regulating organ - which easily make up half the value of the movement - manufactured in Switzerland. Its case, bracelet, glass, crown and cheaper components can be made in the Far East for example. For this reason some image-conscious watch companies are calling for a recognized certificate of origin that guarantees 100% Swiss manufacture. Until 1971, there were no rules governing the use of Swiss Made. To close this loophole, it was decreed that any watch with a movement assembled in Switzerland was entitled to have Swiss Made on its dial, irrespective of where it was cased up. The other components, such as the case and bracelet, were not included in the law. A study launched in 1986 was to have established new criteria for the component parts of a watch. Two years later it was decided - in consultation with the relevant professional associations - to maintain the 1971 status quo. In 1990 discussions on a revised version were resumed, resulting in the Swiss Made ordinance of 27 May 1992. Foreign companies that based their production on the earlier regulations, were given until 30 June 1997 to comply. From then on non-Swiss producers could no longer use Swiss Made if the watch is not put together in Switzerland, even though all the parts are manufactured in Switzerland. 
 
Table roller Disc, mounted on the balance-shaft, carrying the impulse pin which moves the lever.

Tachometer scale A scale on the dial of chronographs that converts elapsed time to average speed. The chronograph is used to time a vehicle over a measured kilometre or a mile. The stopped chronograph hand points to the average speed of the vehicle in kph or mph over the distance.

Telemeter scale A chronograph scale used to determine distance from the speed of sound. For example the distance of a storm can be found by starting the chronograph on a flash of lightning and stopping it when the thunder is heard. The distance is read off against the chronograph hand on the scale, which can be calibrated in miles or in kilometres. Soldiers in battle have found telemeter scales useful for calculating the distance of enemy fire by timing the period between the muzzle-flash and the sound of the shot.

Three-quarter plate A movement construction common to English, American and German watches in which the going-train is held under a single large plate, instead of separate bars and bridges. Only the balance and escapement are exposed to view.

Time zones Each 15° of longitude east or west of the Greenwich meridian (0° longitude) represents a time difference of one hour. Time-zone watches show the local times in two or more time zones of the world, either by using several movements in a single case or by an additional complication. World Time watches show the time in all 24 zones.

Timing positions Watches are adjusted in various positions. Wristwatches, which are worn in changing positions, are adjusted dial down and crown down. Precision watches are usually timed and adjusted in five positions: crown left, crown up, crown down, dial up and dial down.

Tourbillon carriage A delicate and light cage of steel or titanium in which the balance and spring, lever and escapement are mounted and rotated.

Tourbillon  Invented in 1795 and patented in 1801 by Abraham-Louis Breguet to compensate for positional errors in the balance and balance-spring of a watch. The tourbillon (whirlwind) places the entire balance and escapement in a rotating cage, constructed as lightly as possible. The cage revolves on its axis at a fixed rate - usually once a minute - thereby averaging out the gravitational effects on the balance of a watch in an upright position, and improving its rate. The tourbillon has no effect on the accuracy of a watch when it is placed horizontally.
Trench watch (see wristlet) Early military watches particularly from World War 1, with wire lugs

Trimming The removal of all machining traces.

Tuning-fork watch A watch with an electrically driven vibrating fork as a regulating organ. The best known model is Bulova's patented "Accutron" from the fifties.

Twenty-four-hour indication In which the hour-hand goes around its axis once every 24 hours, indicating all the hours of the day and night on the dial. It is rare because it needs getting used to. The first wristwatches with 24-hour indication date from World War 1. Additional 24-hour indications on a 12-hour dial are found in GMT models for a different time-zone.

Under-dial work The train of wheels between the base plate and the dial that transmits the rotation of the centre (minute) arbor to the hour-hand. The under-dial work also allows the hands to be set by the crown in its pulled-out position.

Watch cases The movement's protective housing is made in a wide variety of forms and materials. Sealed and water-resistant cases are used for wristwatches in many different forms: round, square, oval, rectangular, tonneau and cushion-shaped.

Watch-glasses Wristwatches have several sorts: Crystal: scratch-resistant but very fragile; usually found in older watches. Synthetic (Acrylic glass): unbreakable, but easily scratched (from the 1940s). Mineral glass: with a hardness of 5Mohs it is much more scratch-resistant than synthetic watch-glass. Sapphire crystal: hardness, 9Mohs; scratch-proof, not easily broken and can only be cut by special diamond-tipped tools.

Watch manufacturers/retailers:
AeroWatch
Alfex
Andre Le Marquand
Angular Momentum
Audemars Piguet
Auguste Reymond
Pierre Balmain
Baume et Mercier
Bedat & Co.
Bell & Ross
Berney-Blondeau
Bertolucci
Blancpain
Boucheron
Bonneville
Breguet
Breitling
Bulgari
Bulova
Bunz
Camera Cuss
Candino
Cartier
Carven
Casio
Catamaran
Catena
Catorex
Century Time
Gems
Certina
Chagal
Chanel
Charriol
Chase-Durer
Chopard
Citizen
Clerc
Concord
Corum
Consul
Daniel
JeanRichard
David Yurman
Delbana
Delma
Doxa
Dubey & Schaldenbrand
Ebel
Eberhard
Endura
Enigma
Epos
ETA
Eterna
Fendi
Festina
Fortis
Frederique Constant
Furrer-Jacot
Garrards
Girard-Perregaux
Glycine
Goldsmiths & Silversmiths
Grenacher
Grovana
Gucci
Hanowa
Harry Winston
Horoswiss
Hublot
Ikepod
Its Time
IWC
Jaeger-LeCoultre
Jean d'Eve
Jean Marcel
Jovial
J.W.Benson
Kreiger
Leschot
Limes
Longines
Luminox
Mahara MHR
Mappin
Mauboussin
Maurice Lacroix
Mellerio/Mellers
Michel Jordi
Mido
Furrer-Jacot
Milus
Minerva
MOMO Design
Mondaine
Montblanc
Mont d' Or
Movado
North Eagle
Officine Panerai
Omega
Oris
Omega
Parmigiani
Patek Philippe
Paul Picot
Perrelet
Piaget
Pierre Laurent
Piquot Meridie
Porsche Design
Pulsar
Rado
Rama
Raymond Weil
Reuge
RGM
Revue Thommen
Roamer
Roberge
Rodolph
Rolex
Rotary
Roventa-Henex
Saint Honore
Sarcar
Sector
Seiko
Sidewatch
Skagen
Spoon
Swatch
The Swatch Group
Swiss Army
Swiza
TAG-Heuer
Technomarine
Temption
Timex
Tissot
Titoni
Tudor
Ulysse Nardin
Universal
Vacheron Constantin
Van der Bauwede
Ventura
Vincent Calabrese
Victorinox
Waltham
Wenger
Wittnauer
Xemex
Zenith
Zitura
Zodiac

Waterproof Beware if a watch is described as waterproof as this would not be the case. No watch is considered 100% Water Proof and watches are not allowed to be termed as such. See Water Resistant for correct terminology)

Water-resistant wristwatches Originally a watch case was deemed "waterproof" if it withstood perspiration, splashes, rain or immersion in one meter of water for 30 minutes. Higher limits are often expressed in the test figures (depth in water, atmospheres or bars) on the case or the dial. Diver's watches are subject to stricter norms - the ability to withstand daily use for at least one hour at a depth of 100 meters. Wristwatches able to withstand depths of 200 meters or more have now become almost commonplace among the major manufacturers.

White Gold An 18k alloy of yellow gold with nickel or similar metal

Wristlet  The term used in the early 1900s, particularly during World War 1, for watches worn on the wrist.

Yellow Gold  Either 14k or 18k. The traditional gold used in watch making in both all gold or bi-metal combinations.