Helpful Terms to Know

• 12-HOUR RECORDER (REGISTER): A subdial on a chronograph that can time periods of up to 12 hours.
• 30-MINUTE RECORDER (REGISTER): A subdial on a chronograph that can time periods of up to 30 minutes.
• ACRYLIC CRYSTAL: Made of an inexpensive plastic that can have shallow scratches buffed out.​
• ALARM: A watch complication that sounds an alarm at a preset time or at regular intervals.
• ALTIMETER: A device that determines altitude by responding to changes in barometric pressure.
• ANALOG DISPLAY: A display that shows the time by means of hands and a dial.
• ANALOG WATCH: A watch with a dial, hands, and numbers or markers that present a total display of 12-hour time span. Analog digital refers to a watch that has both a digital display and hands of a conventional watch.
• APERTURE: Small opening. The dials of some watches (in French: montres à guichet) have apertures in which certain indications are given (e.g. the date, the hour, etc).
• ARDILLON BUCKLE: Regular two piece buckle used to attach a leather strap, like the buckle on a belt.
• ASSEMBLING: Process of fitting together the components of a movement. This was formerly done entirely by hand, but the operations have now been largely automated. Nevertheless, the human element is still primordial, especially for inspection and testing.
• ATMOSPHERE (ATM): A unit of measurement used to indicate the water resistance of a watch. One atmosphere equals 10 meters (33 feet).
• AUTOMATIC MOVEMENT: A mechanical movement that requires no winding because the rotor, part of the automatic mechanism, winds the mainspring every time you move your hand. The first automatic movement was invented in Switzerland by Abraham-Louis Perrelet in the Eighteenth century. When fully wound and left to sit, most automatics have up to 36 hours of reserve power. Mechanical movements are accurate within one minute each day. Automatic movements have gained in popularity the last few years especially with watch connoisseurs and are considered to be Switzerland’s mechanical answer to the popularity of the no-winding-needed quartz movements that are standard in Japanese watches.
• AUTO REPEAT COUNTDOWN TIMER: A countdown timer that resets itself as soon as the preset time has elapsed and starts the countdown again. It repeats the countdown continuously until the wearer pushes the stop button.
• AUTOMATIC WATCH: A watch whose mainspring is wound by the movements or accelerations of the wearer’s arm. On the basis of the principle of terrestrial attraction, a rotor turns and transmits its energy to the spring by means of an appropriate mechanism. The system was invented in Switzerland by Abraham-Louis Perrelet in the 18th century.
• AUTOMATIC WINDING: Also called “self-winding”, this is winding that occurs through the motion of the wearer’s arm rather than through turning the winding stem. It works by means of a rotor that turns in response to motion, thereby winding up the watch’s mainspring. An automatic watch that is not worn for a day or two will wind down and need to be wound by hand to get it started again.
• BALANCE SPRING: A very fine spring (also called a “hair spring”) in a mechanical watch that returns the balance wheel back to a neutral position.
• BALANCE WHEEL: The heart of the movement that receives the energy to run from the escapement. The balance wheel beats, or oscillates, in a circular motion between five and ten times per second.
• BARREL: Thin cylindrical box containing the mainspring of a watch. The toothed rim of the barrel drives the train.
• BASE METAL: Any non-precious metal.
• BATTERY: A device that converts chemical energy into electricity. Most watch batteries are silver oxide type delivering 1.5 volts. Much longer lasting lithium batteries are 3 volts.
• BATTERY RESERVE INDICATOR: See “power reserve indicator”.
• BEZEL: The surface ring on the watch that surrounds and holds the crystal in place. A rotating ratchet bezel moves in some sport watches as part of the timing device. If rotating bezels are bidirectional (able to move clockwise or counter-clockwise) they can assist in calculations for elapsed times or for tracking different time zones.
• BI-DIRECTIONAL ROTATING BEZEL: A bezel that can be moved either clockwise or counterclockwise. These are used for mathematical calculations or for keeping track of elapsed time.
• BRACELET: Flexible metal band consisting of assembled links, usually in the same style as the case. Detachable links change the length of the bracelet.
• BRIDGE: Complementary part fixed to the main plate to form the frame of a watch movement. The other parts are mounted inside the frame.
• CABOCHON CROWN: A winding crow set with a precious or semiprecious stone, usually sapphire, spinnel, or diamond.
• CALENDAR: A complication on a watch that displays the date.
• CALIBER: A term used to differentiate different types of movements made by the same manufacturer.
• CAMBERED: Refers to a curved or arched dial or bezel.
• CARAT: The physical weight of a gemstone.  Carat is a measure of weight.
• CASE: The body of the watch that contains the movement and dial.
• CASEBACK: The reverse side of a watch case that lies against the skin. May be transparent to allow viewing of the inner workings of the watch or be solid. Most manufacturers engrave casebacks with their name, water and shock resistance, case metal content and other details.
• CHIME: The bell-like sound made when a clock strikes on the hour, half hour, etc. Two familiar chimes traditionally found in clocks are the Westminster chime made by the famous Big Ben in London, and the bim bam, a two note chime.
• CHRONOGRAPH: A stopwatch, i.e., a timer that can be started and stopped to time an event. There are many variations on the chronograph. Some operate with a center seconds hand which keeps time on the watch’s main dial. Others use subdials to elapsed hours, minutes and seconds. Still others show elapsed time on a digital display on the watch face. When a chronograph is used in conjunction with specialized scales on the watch face, it can perform many different functions, such as determining speed or distance. Some chronographs can time more than one event at a time. Do not confuse the term “chronograph” with “chronometer”. The latter refers to a timepiece, which may or may not have a chronograph function, that has met certain high standards of accuracy set by an official watch institute in Switzerland. Watches that include the chronograph function are themselves called “chronographs”.
• CHRONOMETER: A movement certified by an independent testing agency called C.O.S.C. (Contrôle Officiel Suisse des Chronomètres) and is known to be 99% accurate over a fifteen day period in a variety of simulated wearing positions and different temperatures.
• CLASP: Refers to a hinged metal buckle that attaches a metal bracelet or leather strap.
• COMPLICATION: Any feature on a watch beyond the display of the time.
• COSC: The official Swiss Chronometer Testing Institute that puts every chronometer watch through a rigorous, 15-day testing procedure to verify the watch’s precision.
• COUNTDOWN TIMER: A feature found predominantly on quartz watches that allows the user to set an allotted time in hours and minutes and have an alarm ring when that time period expires.
• CROWN:  The round knob on the side of watch used to adjust time and date and wind the movement on a mechanical watch, giving it operating power.
• CRYSTAL: The clean cover over the watch face. Three types of crystals are commonly found in watches:
• 1. Acrylic crystal made of an inexpensive plastic that can have shallow scratches buffed out. 2. Mineral crystal- comprised of several elements that are heat-treated to create unusual hardness for scratch resistance. 3. Sapphire crystal- the most expensive and durable of the crystals. A non-reflective coating on some sport styles prevents glare.
• DAY-DATE:  Complication on a watch that displays the day and date.
• DAY/NIGHT INDICATOR: A colored or shaded band on a world time that shows which time zones are in daylight and which in darkness.
• DEPLOYANT BUCKLE:  Invented by Cartier in the early 20th century, a leather strap attached to a folding metal buckle that is considered more secure to wear than a regular Ardillon buckle. Should the buckle open up, the watch is still attached to the wrist.
• DEPTH ALARM:  An alarm on a diver’s watch that sounds when the wearer exceeds a pre-set depth. In most watches it stops sounding when the diver ascends above that depth.
• DIAL:  The watch face. The numerals, indices, or surface design are usually applied; others have been printed on.
• DIGITAL DISPLAY:  Can refer to either a LCD display on a quartz watch or oversized numerals indicating date or time on a mechanical watch.
• DIGITAL WATCH: A watch that shows the time through digits rather than through a dial and hands display.
• DIRECT-DRIVE: A function that allows the second-hand to advance in intervals rather than a smooth sweep for more precise timekeeping. The French term for a direct-drive second hand is a trotteuse.
• DUAL TIMER: A watch that measures current local time as well as at least one other time zone. The additional time element may come from a twin dial, extra hand, subdials, or other means.
• DIVER’S WATCH: A type of watch that has exceptional water resistance and is usually equipped with a unidirectional diver’s bezel to assist in recording dive time. A diver’s watch may also have a helium escape valve, screw down crown, and extension bracelet.
• ELAPSED TIME ROTATING BEZEL: A graduated rotating bezel used to keep track of periods of time. The bezel can be turned so the wearer can align the zero on the bezel with the watch’s seconds or minutes hand. He/she can then read the elapsed time off the bezel. This saves him/her having to perform the subtraction that would be necessary if he used the watch’s regular dial.
• END OF LIFE (EOL) INDICATOR: A feature on a quartz watch that causes the second hand to jump in five second intervals when the battery is nearly exhausted. The end of life indicator serves as a reminder to replace the battery when necessary.
• ENGINE TURNING: Decorative engraving, usually on the watch face.
• ESCAPEMENT: Device in a mechanical movement that controls the rotation of the wheels and thus the motion of the hands.
• ETA: One of the leading manufacturers of watch movements based in Switzerland. ETA movements are used by many major Swiss watch brands.
• FACE: The visible side of the watch where the dial is contained; most are printed with Arabic or Roman numerals.
• FLYBACK (RETOUR EN VOL): A function particularly useful to pilots that allows the chronograph hand to be reset to zero and immediately started again by pressing once on the push piece.
• FREQUENCY: The number of vibrations per second, in hertz (Hz).
• GASKET: Most water resistant watches are equipped with gaskets to seal the case back, crystal, and crown to protect against water infiltration during normal wear. It is important to have the gaskets checked every two years to maintain the water resistance of the watch.
• GENEVA SEAL: A quality seal awarded by an independent bureau in Geneva to watch movements submitted to it for inspection. To receive the seal, a movement must meet 12 criteria related to the quality of the movement’s finishing and the materials from which it is made. It must also have been manufactured in the canton of Geneva. The seal, which consists of the Geneva coat of arms, is stamped on the movement. The Geneva Seal is also called the “Geneva Hallmark” or the “Poinçon de Genève” (stamp of Geneva).
• GEAR TRAIN: The system of gears which transmits power from the mainspring to the escapement.
• GENEVA WAVES: Decorative stripes on the plates, bridges, cocks or rotors of many watches. Geneva waves are also called “Geneva stripes” or “côtes de Genève” (Geneva ribbing).
• GMT (GREENWICH MEAN TIME): The GMT has an additional hour hand that shows two different time zones.
• GOLD: A yellow precious metal that is stainless and very malleable. It is used in alloys to make jewelry, bracelets and watches. The portion of gold in the alloy is indicated in carats (K).
• GOLD PLATING: A layer of gold that has been electro-deposited onto a metal; its thickness is measured in microns.
• GRANDE SONNERIE: A type of repeater that sounds the hours and quarter hours when the wearer pushes the button.
• GUILLOCHÉA: type of decorative pattern, such as barleycorn or sunburst, found on some watch dials and plates. Genuine guilloché is produced using an elaborate engraving machine and is also known as “engine turning.” Guilloché can also be simulated with a less-expensive stamping process.
• HACKING SECONDS: Also known as hack or stop seconds. A watch that “hacks” or that has “hacking seconds” is one in which the seconds hand stops when the crown is pulled out. Hacking is typically achieved when pulling the crown out to the time-setting position causes a brake or lever to come into contact with the rim of the balance wheel, causing it to stop and to be held in position. Hacking allows the watch to be more easily set to a reference signal, or synchronized with second timepiece. Pushing the crown in releases the brake or lever, allowing the balance wheel to move freely.
• HAIRSPRING: Also called a balance spring, this is the extremely thin, coiled spring that controls the swings, or oscillations, of the balance. The inner end of the hairspring is attached to the balance staff and the outer end to a stud on the balance cock. The spring’s elasticity ensures that the balance swings back and forth at a regular rate. The active length of the hairspring interacts with the momentum of the balance rim to determine the duration of each beat of the balance. This is why most watches are equipped with a regulator on the balance cock that can be adjusted to vary the active length of the hairspring. Lengthening the spring causes the watch to run more slowly; shortening it makes the watch run faster
• HALLMARK: A mark stamped on the case of a watch to provide information about the degree of purity of the precious metal used, the country (and sometimes city) of origin, the year of manufacture and the identity of the case’s maker. Additional hallmarks may show the trademark of the watch company, a reference number and a serial number.
• HANDS: The pointing device anchored at the center of and circling around the dial indicating hours, minutes, seconds and any other special features of the watch.
• HARD METAL: A scratch resistant metal comprised of binding several materials, including titanium and tungsten carbide, which are then pressed into an extremely hard metal and polished with diamond powder to add brilliance.
• HIGH-TECH CERAMIC: Used as a protective shield for space crafts reentering the earth’s atmosphere, high-tech ceramic is polished with diamond dust to create a highly polished finish. As the ceramic can be injection molded, pieces can be contoured. It has a very smooth surface, usually found in black but can be produced in a spectrum of colors.
• HOROLOGY: The science of time measurement, including the art of designing and constructing timepieces.
• INDEX: An hour indicator on an analog watch dial, used instead of numerals.
• INTEGRATED BRACELET: A watch bracelet that is integrated into the design of the case.
• JEWELS: Synthetic sapphires or rubies that act as bearings for gears of a mechanical watch. A quality hand wound or automatic mechanical watch contains at least 17 jewels.
• JUMP HOUR INDICATOR: A jump hour indicator takes the place of an hour hand. It usually shows the hours by means of a numeral in a window.
• KARAT (CARAT): A unit of gold fineness (and gemstone weight). 24K is pure gold, whereas 18K gold is 75% pure.
• LAP MEMORY: The ability, in some quartz sport watches, to preserve in the watch’s memory the times of laps in a race that have been determined by the lap timer. The wearer can recall these times on a digital display by pushing a button.
• LAP TIMER: A chronograph function that lets the wearer time segments of a race. At the end of a lap, he/she stops the timer, which then returns to zero to begin timing the next lap.​
• LAVALIER: An ancestor of pendant, or tie, imagined by the duchesse de la Vallière in the 17th century, this large scarf tied in a bow was frequently worn by elegant folk in the 19th century before losing its puffed up bravado to a simpler and more traditional knot. For very formal occasions, it is still worn today, like the Ascot tie, but differs to its cousin with a smooth central ribbon secured with a tie pin.
• LIMITED EDITIONS: A watch style manufactured in a specific amount, often numbered, and available in limited quantities. Limited editions are available from most fine watch manufacturers and may be highly prized by collectors.
• LIQUID-CRYSTAL DISPLAY: A digital watch display that shows the time electronically by means of the liquid held in a thin layer between two transparent plates.
• LUGS: Extensions on either side of the bezel where the bracelet or strap is attached.
• LUMINOUS: Self-illuminating paint used on hands and markers.
• MAIN PLATE: Base plate on which all the other parts of a watch movement are mounted.
• MAINSPRING: The driving spring of a watch or clock, contained in the barrel.
• MANUAL WIND: A manual wind watch must be wound every day by the crown in order to run. Even with that inconvenience, they are still produced by the major houses in Switzerland. Some of the most beautiful pieces made today are manual wind, and you actually won’t fund many value or budget manual winds (but they exist!). With exhibition backs becoming very common, it’s nice to view the active movement without a rotor in the way.
• MARINE CHRONOMETER: Highly accurate mechanical or electronic timekeeper enclosed in a box (hence the term box chronometer), used for determining the longitude on board ship.  Marine chronometers with mechanical movements are mounted on gimbals so that they remain in the horizontal position is necessary for their precision.
• MEASUREMENT CONVERSION: A feature, usually consisting of a graduated scale on the watch’s bezel, that lets the wearer translate one type of measurement into another — miles into kilometers, for instance, or pounds into kilograms.
• MECHANICAL MOVEMENT:A movement based on a mainspring that is wound by hand. When wound, it slowly unwinds the spring in an even motion. An automatic mechanical requires no winding because of the rotor, which winds the mainspring every time you move your wrist. Click here to learn more about how mechanical watches work.
• MICRON: Unit of measurement of the thickness of the gold-coating. 1 micron = 1/1000mm.
• MILITARY TIME (24-HOUR TIME): Time 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.
• MINERAL CRYSTAL: Watch glass that has been tempered to increase its scratch resistance.
• MINUTE REPEATER:A complication on a watch that can strike the time in hours, quarters, or seconds by means of a push piece.
• MOONPHASE: An indicator that keeps track of the moon’s phases. A regular rotation of the moon is once around the earth every 29 days, 12 hours, and 44 minutes. Once set, the moonphase indicator accurately displays the phase of the moon.
• MOTHER-OF-PEARL: An iridescent, milky interior shell of the fresh water mollusk that is sliced thin and used on watch dials. While most have a milky white luster, mother-of-pearl also comes in other colors such as silvery gray, gray blue, pink, and salmon.
• MOVEMENT: The engine of the watch, a movement is either quartz or mechanical.
• MYSTERY WATCH: A patented invention of watchmaker Vincent Calabrese and produced by Jean Marcel, a Swiss manufacturer, the Mystery automatic mechanical watch uses no hands to indicate hours, minutes or seconds. Rather a jumping hour window moves clockwise around a minute scale while a second indicator, an arrow, also ticks around. Gently breathing on the crystal causes the word “mystery” to appear.
• OSCILLATION: The travel of the balance wheel from one extreme to the other and back again.
• PALLET: One of two small pins in a lever escapement that mesh with the teeth of the escape wheel. Pallets are usually made of synthetic ruby.
• PEDOMETER: A device that counts the number of strides taken by the wearer by responding to the impact of the wearer’s steps.
• PERLAGE: A type of decoration applied to watch movements. It consists of small, overlapping circles. The word is French and means, literally, “pearling.”
• PERPETUAL CALENDAR: A type of calendar complication that automatically adjusts for months of different lengths and indicates February 29 in each leap year.
• PINK (OR ROSE) GOLD: A softly hued gold that contains the same materials as yellow gold but with a higher concentration of copper in the alloy. A popular color in Europe, rose gold in watches is often seen in retro styling or in tricolor gold versions. Some 18K red gold watches achieve their color from adding more copper in the alloy.
• PLATE: A flat piece of metal, typically disk-shaped, that serves as a foundation for the movement and/or for one or more complications. The “main” or “bottom” plate bears the bridges, cocks and other parts of a movement. The motion work is generally found on its underside. The bridges and cocks are affixed to its upper surface. The plate has threaded holes to accommodate screws as well as smooth holes for the jewels that bear the wheel train’s pivots.
• PLATING: A coating of a metal base with another metal. In watchmaking, a stainless steel base is coated with gold 7 to 20 microns thick.
• PLATINUM: One of the rarest precious metals, platinum is also one of the strongest and heaviest, making it a popular choice for setting gemstone jewelry and watches. It has a rich, white luster and an understated look. Platinum is hypoallergenic and tarnish resistant and is 85-95% pure when used in jewelry and watches. Many platinum watches are produced in limited editions due to the expense and rarity of the metal.
• POWER RESERVE: The time the watch will run with a fully charged power supply. For mechanical watches, it is usually 44 hours whereas for quartz watches it can vary from 18 months to 10 years.
• POWER RESERVE INDICATOR: A feature of a mechanical watch that shows how much longer the watch will operate before it must be wound again.
• PULSIMETER: A scale on a chronograph watch for measuring the pulse rate.
• PUSH-PIECE: Button that is pressed to work a mechanism. (The push-pieces on chronographs, striking watches, alarms, etc.)
• QUARTZ CRYSTAL: A tiny piece of synthetic quartz that oscillates at the rate of 32.768 times a second, dividing time into equal segments.
• QUARTZ MOVEMENT: A movement which allows a watch to keep time without being wound. This technology employs the vibrations of a tiny crystal to maintain timing accuracy. The power comes from a battery that must be replaced about every 1.5 years. In recent years, new quartz technology enables the watch to recharge itself without battery replacement. This power is generated via body motion similar to an automatic mechanical watch, or powered by light through a solar cell, or even by body heat. A digital quartz watch has no mechanical parts. Most quartz movements are made in Hong Kong, Japan or Switzerland.
• RATCHET BEZEL: A bezel ring which can either turn one way (counter clockwise) or both ways and generally clicks into place.
• RATTRAPANTE (SPLIT-SECOND CHRONOGRAPH): A second chronograph that runs concurrently with the first but can be stopped independently to record an intermediate time. It then catches up to run with the first hand again.
• REPEATER: A device that chimes the time when the wearer pushes a button.
• RETOUR EN VOL (FLYBACK): A function particularly useful to pilots that allows the chronograph hand to be reset to zero and immediately started again by pressing once on the push piece.
• ROSE (OR PINK) GOLD: A softly hued gold that contains the same materials as yellow gold but with a higher concentration of copper in the alloy. A popular color in Europe, rose gold in watches is often seen in retro styling or in tricolor gold versions. Some 18K red gold watches achieve their color from adding more copper in the alloy.
• ROTATING BEZEL: A bezel (the ring surrounding the watch face) that can be turned. Different types of rotating bezels perform different timekeeping and mathematical functions.
• ROTOR: The part of an automatic watch that winds the the movement’s main spring.
• SAPPHIRE CRYSTAL: Synthetic corundum crystal with a hardness second only to diamond. Transparent sapphire is used for scratch-resistant watch crystals.
• SCREW-LOCK CROWN: A crown that can be screwed into the case to make the watch watertight.
• SEAL: Synthetic gaskets that seal the joints between parts of the case to keep out moisture.
• SECOND TIME-ZONE INDICATOR: An additional dial that can be set to the time in another time zone. It lets the wearer keep track of local time and the time in another country simultaneously.
• SHOCK ABSORBER: Resilient bearing which, in a watch, is intended to take up the shocks received by the balance staff and thus protects its delicate pivots from damage.
• SHOCK RESISTANCE: The ability to withstand normal wear and tear, even during strenuous sport activities.
• SKELETON CASE: A case with a transparent front or back that allows the wearer to view the watch’s movement.
• SKELETON MOVEMENT: A watch with no dial that exposes the movement.
• SLIDE RULE BEZEL: A rotating bezel that is printed with a logarithmic scale and others and is used with fixed rules of mathematics.
• SOLAR COMPASS: A compass that lets the wearer determine the geographical poles by means of a rotating bezel. The wearer places the watch so that the hour hand faces the sun. He then takes half the distance between the position and 12 o’clock, and turns the bezel until its “south” marker is at that halfway point. Some quartz watches have solar compasses that show directions on an LCD display.
• SOLAR POWERED BATTERIES:  Batteries in a quartz watch that are recharged via solar panels on the watch face. Also known as Solar Cell
• SPLIT-SECOND CHRONOGRAPH (RATTRAPANTE): A second chronograph that runs concurrently with the first but can be stopped independently to record an intermediate time. It then catches up to run with the first hand again.
• SPLIT SECONDS HAND: Actually two hands, one a flyback hand the other a regular chronograph hand. When the wearer starts the chronograph, both hands move together. To time laps or different finishing times, the wearer can stop the flyback hand independently while the regular chronograph hand keeps moving, in effect ”splitting” the hand(s) in two.
• STAINLESS STEEL: An extremely durable metal alloy (chromium is a main ingredient) that is immune to rust, discoloration, and corrosion. Stainless steel can be highly polished, thus resembling a precious metal. Because of its strength, it is often used on watch casebacks that are made of other metals.
• STEPPING MOTOR: The part of a quartz movement that moves the gear train, which in turn moves the watch’s hands.
• STERLING SILVER: A white and highly reflective precious metal. Sterling refers to silver that is 92.5% pure, which should be stamped on the metal, sometimes accompanied by the initials of the designer or country of origin as a hallmark. Although less durable than stainless steel and other precious metals, sterling silver is often used in watches that look like sterling jewelry. A protective coating may be added to prevent tarnish.
• STOPWATCH: A watch with a seconds hand that measures intervals of time. When a stopwatch is incorporated into a standard watch, both the stopwatch function and the timepiece are referred to as a “chronograph”. Subdial: A small dial on the watch face used for any of several purposes, such as keeping track of elapsed minutes or hours on the chronograph or indicating the date.
• STRAP: A watch band made of leather, plastic or fabric.
• SUBDIAL: A small dial used for several purposes, such as keeping track of elapsed minutes or hours on a chronograph, or indicating the date.
• SUN/MOON INDICATOR: A wheel on a watch partially visible through a cut-out window indicating a sun and a moon on a 24-hour basis.
• SWISS MADE: A watch is considered Swiss if its movement was assembled, started, adjusted and controlled by the manufacturer in Switzerland.
• SWISS A.O.S.C. (CERTIFICATE OF ORGIN): A mark identifying a watch that is assembled in Switzerland with components of Swiss origin.
• SWEEP SECONDS-HAND: A seconds-hand that is mounted in the center of the watch dial.
• TACHYMETER (ALSO TACHOMETER): A watch function that measures the speed at which the wearer moves.
• TANG: Classic belt buckle, also known as an Ardillon.
• TANK WATCH: A rectangular watch with heavier bars on either side of the dial, inspired by the tank tracks of World War I and first created by Louis Cartier.
• TELEMETER: A watch function that finds the distance of an object from the wearer by measuring how long it takes sound to travel that distance. Like a tachymeter, a telemeter consists of a stopwatch function and a special scale on the dial of a chronograph.
• TIMER: Instrument used for registering intervals of time (durations, brief times), without any indication of the time of day.
• TITANIUM: The “space age” metal, often with a silvery gray appearance. Because it is 30 percent stronger and nearly 50 percent lighter than steel, it has been increasingly used in watchmaking, especially sport watch styles. Its resistance to salt water corrosion makes it particularly useful in diver’s watches. Since it can be scratched fairly easily, some manufacturers use a patented-coating to resist scratching.
• TONNEAU CASE: A watch with a barrel-shaped case with two convex sides.
• TOTALIZER: A mechanism that keeps track of elapsed time and display it, usually on a subdial.
• TOURBILLON: A device in some mechanical watches that attempts to eliminate timekeeping errors caused by slight variations from shifts in gravity when a watch changes position during use. The round carriage or “cage” of the tourbillon holds the mechanisms that rotate the wheels, and thus the hands of the watch, in a continuous rate of once per minute.
• TRITIUM: An isotope of hydrogen that is used to activate the luminous dots or indices on a watch dial. The radioactivity released in this process is too slight to pose a health risk.
• TWO TONE: A watch that combines two metals, usually yellow gold and stainless steel in the case of fine watches.
• UNI-DIRECTIONAL ROTATING BEZEL: An elapsed time rotating bezel, often found on divers’ watches, that moves only in a counterclockwise direction. It is designed to prevent a diver who has unwittingly knocked the bezel off its original position from overestimating his remaining air supply. Because the bezel moves in only one direction, the diver can error only on the side of safety when timing his dive. Many divers’ watches are ratcheted, so that they lock into place for greater safety.
• VIBRATION: A swing of the balance. A watch vibrating 18,000 times an hour beats five times a second.
• WATERPROOF: An illegal and misused term; no watch is fully 100 percent waterproof.
• WATER RESISTANCE: A watch bearing the inscription “water resistant” on its caseback can withstand light moisture, such as a rainstorm or sink splashes but should not be worn swimming or diving.
  • Watches come in different water resistant depths and diver’s depths:
    • Water resistant: Withstands splashes of water or rain but should not be worn while swimming or diving
    • Water tested to 50 meters (165 feet): Suitable for showering or swimming in shallow water
    • Water resistant to 100 meters (330 feet): Suitable for swimming or snorkeling
    • Water resistant to 150 meters (500 feet): Suitable for snorkeling.
    • Water resistant to 200 meters (660 feet): Suitable for scuba diving
    • Water resistant to 1000 meters (3300 feet): Suitable for professional deep sea diving
• WHITE GOLD: Created from yellow gold by adding either nickel or palladium to the alloy to achieve a white color. Most watches made of white gold are 18K.
• WINDING: Operation consisting in tightening the mainspring of a watch. This can be done by hand (by means of the crown) or automatically (by means of a rotor, which is caused to swing by the movements of the wearer’s arm).
• WINDING STEM: The button on the right side of the watch case used to wind the mainspring. Also called a “crown.”
• WORLD TIME DIAL: A dial, usually on the outer edge of the watch face, that tells the time up to 24 time zones around the world. The time zones are represented by the names of cities printed on the bezel or dial. The wearer reads the hour in a particular time zone by looking at the scale next to the city that the hour hand is pointing to. The minutes are read as normal. Watches with this feature are called “world timers”.
• WORLD TIMER: A watch with a dial that indicates up to 24 time zones around the world, usually found on the outer edge of the face or sometimes on the bezel. Time zones around the world are indicated by major cities.
• YYACHT TIMER: A countdown timer that sounds warning signals during the countdown to a boat race.
• YELLOW GOLD: The traditional and popular color gold used in all gold or gold and stainless steel or other precious metal combinations. Yellow gold watches may be found in 14K or, as found from most European manufacturers, 18K.