A

Acrylic Crystal

Acrylic crystal is a type of plastic once widely used as watch glass before sapphire and mineral crystals became common. It is lightweight and shatter-resistant but scratches more easily than harder materials.

Alarm

An alarm is a complication that allows a watch to produce a sound at a preset time. This feature appears mostly in quartz watches, though a few mechanical models include it as well.

Amplitude

Amplitude refers to the angle through which the balance wheel swings during each oscillation. In a healthy mechanical movement, this typically falls somewhere between about 275° and 315°.

Ana-digi

Short for analogue-digital, this describes watches that combine traditional hands with a digital display. These designs are usually powered by quartz movements.

Analogue

An analogue time display uses moving hands that travel around a dial to show the time. It is the traditional method used in most mechanical and many quartz watches.

Anglage

Anglage is a finishing technique where the edges of movement parts are carefully bevelled and polished. The angled edge improves appearance and removes sharp corners from the component.

Annual Calendar

An annual calendar is a complication that automatically adjusts the date for months with 30 or 31 days. The watch still needs manual correction once per year at the end of February.

Anti-Magnetic

A watch described as anti-magnetic is designed to resist the effects of magnetic fields. Magnetic exposure can disrupt the balance spring and cause a watch to run inaccurately. Anti-magnetic watches use special alloys or shielding to reduce this risk. 

Aperture

An aperture is a small opening in the dial that reveals information such as the date or day from a rotating disc beneath it.

Applied Indices

Hour markers that are attached separately to the dial rather than printed directly onto it. They are often made of metal and may be polished, faceted, or filled with luminous material.

ATM

ATM (atmospheres) is a pressure rating used to indicate water resistance. One atmosphere roughly equals the pressure at 10 metres of water depth, meaning a watch rated to 10 ATM is generally considered suitable for swimming.

Automatic

An automatic movement winds itself through the motion of the wearer’s wrist. A rotating weight inside the watch spins as the wrist moves, tightening the mainspring and storing energy for the movement.

B

Balance Wheel

The balance wheel is the component that regulates time in a mechanical watch. Working with the hairspring, it swings back and forth at a steady rate, controlling how energy moves through the movement.

Balance Spring (Hairspring)

A thin coiled spring is attached to the balance wheel. It controls the oscillation of the balance and plays a central role in regulating a mechanical watch.

Barrel

The barrel is the cylindrical component that contains the mainspring. As the mainspring unwinds, the barrel releases stored energy to power the movement.

Base Plate

The base plate is the structural foundation of a watch movement. Most of the movement’s components are mounted on it, with bridges holding the parts in place.

Bead-Blasting

Bead-blasting is a finishing technique that creates a matte surface by directing fine glass beads at metal under pressure.

Beat

A beat is one movement of the balance wheel in a single direction. Mechanical watches operate at different beat rates, commonly measured in beats per hour.

Bevelled Edges

Bevelled edges are angled and polished edges applied to movement parts. This finishing technique improves appearance and removes sharp corners from the component.

Bezel

The bezel is the ring surrounding the watch crystal. On some watches it rotates and carries markings used for functions such as dive timing or tracking a second time zone.

Bi-Directional Winding

An automatic winding system where the rotor winds the mainspring while rotating in both directions.

Bluing

Bluing is a finishing process that turns steel parts blue through controlled heating or chemical treatment. It protects the metal from corrosion while adding decorative contrast.

Bottom Plate

Another name for the base plate of a movement. It forms the lower structural layer on which the rest of the movement is assembled.

BPH (Beats Per Hour)

BPH indicates how many beats the balance wheel completes in one hour. Common mechanical watch frequencies include 18,000, 21,600, and 28,800 beats per hour.

Bracelet

A bracelet is a metal watch band made from interconnected links that attach the watch case to the wrist.

Breguet Overcoil

A hairspring design where the outer coil curves upward and inward. This shape allows the spring to expand and contract more evenly, improving the stability of the balance wheel’s oscillation.

Bridge

A bridge is a metal plate used to secure specific components of a movement to the base plate. It is fixed with screws and helps hold gears and other parts in position.

Brushing

Brushing is a surface finish created by running abrasive tools across metal, producing fine parallel lines that give the surface a satin appearance.

Buckle

A buckle is a fastening mechanism used on straps made from leather, rubber, or fabric. A small pin secures the strap through one of several adjustment holes.

C

C.O.S.C.

C.O.S.C. stands for Contrôle Officiel Suisse des Chronomètres, the Swiss organization responsible for testing and certifying the accuracy of watch movements. Movements that pass these tests are allowed to carry the chronometer designation.

Calendar

A calendar is a complication that displays date information on a watch, such as the day, date, month, or year, depending on the complexity of the mechanism.

Caliber / Calibre

Caliber (or calibre) refers to a specific movement model used inside a watch. Manufacturers assign caliber numbers or names to distinguish different movement designs.

Case

The case is the outer housing of the watch that protects the movement, dial, and hands. It is usually made from materials such as stainless steel, titanium, gold, or ceramic.

Caseback

The caseback is the rear cover of the watch case. It may be pressed into place or screwed down and can be solid metal or fitted with a transparent window that reveals the movement.

Centrelinks

Centrelinks are the middle sections of a multi-piece bracelet link. They often contrast in finish with the outer links.

Ceramic Case

A watch case made from advanced ceramic material. Ceramic cases are valued for their scratch resistance, light weight, and resistance to corrosion.

Chapter Ring

A chapter ring is a ring positioned around the outer edge of the dial, usually carrying minute or seconds markers.

Chronograph

A chronograph is a complication that allows a watch to function as a stopwatch, measuring elapsed time using additional hands and pushers.

Chronometer

A chronometer is a watch or movement that has passed official accuracy testing by an independent authority such as C.O.S.C.

Chronometer Certified

A movement described as chronometer certified has met the strict accuracy standards required by an official testing body.

Clasp

A clasp is the folding mechanism used to secure a metal bracelet around the wrist.

Co-Axial Escapement

A type of escapement invented by George Daniels that reduces friction in the movement by separating the locking and impulse functions. This design improves efficiency and can extend service intervals.

Cock

A cock is a small metal support fixed to the movement at one end only. It is commonly used to hold the balance wheel in place.

Column Wheel

A column wheel is a precisely machined component used in certain chronograph movements. It coordinates the start, stop, and reset functions of the chronograph.

Complication

A complication is any feature in a watch movement beyond the basic display of hours, minutes, and seconds.

COSC Chronometer

A COSC chronometer is a watch movement that has passed accuracy testing by the Swiss chronometer testing authority. To receive certification, the movement must meet strict daily rate tolerances across multiple positions and temperatures.

Côtes de Genève

A decorative finishing technique applied to movement plates, consisting of repeating striped patterns engraved into the surface. Also known as Geneva stripes.

Crown

The crown is the small knob on the side of a watch used to set the time and date and to wind mechanical movements.

Crown Guards

Crown guards are protective extensions of the case designed to shield the crown from impacts.

Crystal

The crystal is the transparent cover placed over the dial. Modern watches typically use sapphire crystal, while older models may use acrylic or mineral glass.

Cyclops Lens

A small magnifying lens placed on the watch crystal above the date window to enlarge the date display.

Cushion Case

A cushion case is a watch case shape with rounded corners, sitting between a square and a round design.

D

Date

A date complication displays the day of the month, usually as a number shown through a small window on the dial or on a rotating disc.

Day

A day complication displays the day of the week, typically written in full or abbreviated form on the dial.

Dead-Beat Seconds

Dead-beat seconds describes a seconds hand that moves in clear one-second steps rather than in a smooth sweep. This motion is common in quartz watches and rare in mechanical movements.

Decimal Repeater

A decimal repeater is a striking complication that sounds the hours, the number of ten-minute intervals since the hour, and the remaining minutes using a series of gongs.

Decoration

Decoration refers to the finishing techniques applied to watch components to improve their visual appearance. Examples include polishing, brushing, and engraved patterns.

Deployant Clasp

A deployant clasp is a folding metal mechanism used on leather or rubber straps. It allows the strap to open and close securely while reducing wear compared to a traditional buckle.

Dial

The dial is the face of the watch where time and other functions are displayed. It typically carries the hands, indices, and complications.

Display Back

A display back is a caseback fitted with a transparent window that allows the movement inside the watch to be viewed.

Diver’s Extension

A diver’s extension is an additional folding section built into some metal bracelets. It allows the watch to be worn over a wetsuit without adjusting the bracelet length.

Diver’s Watch

A diver’s watch is designed for underwater use and built to meet specific standards for water resistance, visibility, and durability.

DLC (Diamond-Like Carbon)

DLC is a hard carbon-based coating applied to metal surfaces. It creates a dark finish while improving scratch resistance and durability.

Double Axis Tourbillon

A double axis tourbillon rotates the escapement on two different axes. This complex mechanism is intended to further reduce the effect of gravity on timekeeping.

Double Chronograph (Rattrapante)

A double chronograph uses two seconds hands to measure split times. One hand can be stopped to record an intermediate time while the other continues running.

Dauphine Hands

Dauphine hands are faceted watch hands with a sharp, triangular shape. They are often polished to reflect light clearly against the dial.

Day-Date

A day-date complication displays both the day of the week and the numerical date on the dial.

Dual Time

A dual time watch allows the wearer to track two different time zones simultaneously, usually through an additional hour hand or separate display.

E

Endlinks

Endlinks are the pieces that connect a bracelet to the watch case. They fit between the lugs and hold the bracelet in place using spring bars.

Equation of Time

The equation of time is a rare complication that shows the difference between apparent solar time (based on the position of the sun) and mean solar time, which is the standardized time used in daily life.

Escape Wheel

The escape wheel is a gear within the escapement that interacts with the pallet fork. It releases the movement’s stored energy in small, controlled steps.

Escapement

The escapement is the mechanism that regulates how energy from the mainspring flows through the movement. It works with the balance wheel and pallet fork to release energy in precise intervals, allowing the watch to keep time.

Exhibition Back

An exhibition back is a caseback fitted with a transparent window that allows the movement inside the watch to be seen. It is also commonly called a display back.

Engine-Turned Dial

An engine-turned dial features decorative patterns created using a mechanical engraving technique. These patterns are often seen in traditional guilloché-style designs.

Ebauche

An ébauche is a partially assembled movement supplied by a movement manufacturer and later finished or modified by a watch brand.

F

Finish

Finish refers to the surface treatment applied to watch components to change their appearance or texture. Common examples include polished finishes that create a mirror-like surface, brushed finishes that produce fine parallel lines, and bead-blasted finishes that create a matte texture.

Five-Minute Repeater

A five-minute repeater is a striking complication that chimes the hours and the number of five-minute intervals that have passed since the hour. When activated, small hammers strike gongs inside the watch to produce the sound.

Fluted Bezel

A fluted bezel features a series of evenly spaced grooves around its outer edge. The design originally helped watchmakers screw the bezel securely onto the case, though today it is mainly used as a decorative element.

Flyback

A flyback chronograph allows the chronograph seconds hand to instantly reset to zero and restart while timing is still running. This function was originally developed for pilots who needed to measure consecutive time intervals quickly.

Flying Tourbillon

A flying tourbillon is a variation of the tourbillon in which the rotating cage is supported from only one side of the movement. Because there is no bridge covering the top, the mechanism appears suspended and fully visible.

Foudroyante

Foudroyante, sometimes called a lightning seconds display, is a chronograph feature that divides each second into several rapid increments. The hand typically jumps several times per second, allowing more precise measurement of short time intervals.

Four-Year Calendar

A four-year calendar is a complication that displays the date, day, and month while accounting for the leap year cycle. Because it recognizes leap years, it only requires manual adjustment once every four years.

Frequency

Frequency describes how quickly a watch’s regulating system oscillates. In mechanical watches this refers to how many times the balance wheel vibrates per hour, which affects both the smoothness of the seconds hand and the stability of timekeeping.

Fusee

A fusee is a cone-shaped gear used with a chain connected to the mainspring barrel. As the mainspring unwinds and its force decreases, the fusee compensates by adjusting the leverage of the chain, helping deliver more consistent power to the movement.

Full Calendar

A full calendar displays the day of the week, the date, and the month. Because it does not automatically adjust for shorter months, the date must be corrected manually several times each year.

G

Gasket

A gasket is a sealing ring, usually made from rubber or synthetic materials, placed between parts of a watch case. When compressed, it creates a tight seal that prevents water, dust, and moisture from entering the watch.

Gear Train

The gear train is the series of interconnected gears that transfers energy from the mainspring to the escapement. Each gear reduces or adjusts the speed of rotation so that the hands move at the correct rate.

Geneva Seal (Hallmark of Geneva)

The Geneva Seal is a certification granted to watches that meet strict standards of construction, finishing, and assembly in the Canton of Geneva, Switzerland. It is regarded as one of the most demanding quality certifications in watchmaking.

Geneva Stripes

Geneva stripes are decorative wave-like patterns applied to movement plates and bridges using specialized finishing tools. The pattern is both decorative and traditional in high-end Swiss watchmaking, and is also known as Côtes de Genève.

GMT

GMT stands for Greenwich Mean Time, the historical time standard based on the Prime Meridian in Greenwich, England. In watches, a GMT function allows the wearer to track a second time zone using an additional hand or scale.

Grand Sonnerie

A grand sonnerie is one of the most complex striking complications in watchmaking. The watch automatically chimes the hours and quarters as time passes, and can also repeat the time on demand using small hammers striking internal gongs.

Guilloché

Guilloché is a decorative engraving technique that produces intricate, repeating patterns on a watch dial or movement component. These patterns are traditionally cut using specialized mechanical engraving machines.

Glide Lock

A bracelet adjustment system that allows the wearer to change the bracelet length in small increments without using tools. This mechanism is commonly used on professional dive watches to improve fit over a wetsuit or directly on the wrist.

H

Hacking Seconds

Hacking seconds refers to a feature that stops the seconds hand when the crown is pulled out to set the time. This allows the wearer to synchronize the watch precisely with a reference time.

Hairspring

The hairspring is a very fine coiled spring attached to the balance wheel. As the balance wheel swings back and forth, the hairspring expands and contracts, regulating the rhythm of the movement and helping the watch keep consistent time.

Hallmark

A hallmark is an official stamp applied to precious metals such as gold, silver, or platinum. It verifies the metal’s purity and identifies the authority or assay office that certified it.

Hands

Hands are the indicators mounted at the center of the dial that point to hours, minutes, seconds, or other measurements. Their shape and design vary widely depending on the style of the watch.

Hand-Wound

A hand-wound watch uses a mechanical movement that must be wound manually by turning the crown. This action tightens the mainspring, storing the energy that powers the watch.

Hesalite

Hesalite is a trade name used by Omega for a specialized acrylic crystal. It is lightweight and resistant to shattering, though it can scratch more easily than sapphire.

HEV (Helium Escape Valve)

A helium escape valve allows trapped helium gas to exit the watch during decompression. It was originally developed through collaboration between Rolex and the diving company COMEX for use in professional saturation diving.

Horology

Horology is the study and science of timekeeping and the design of clocks and watches.

I

Incabloc

Incabloc is a shock-protection system designed to protect the delicate pivots of the balance wheel. It uses a small spring-mounted setting that allows the jewel to move slightly during an impact, reducing the risk of damage to the movement.

Indices

Indices are the markers placed around the dial to indicate the hours. They may be simple batons, applied metal markers, or other shapes depending on the watch’s design.

Integrated Bracelet

An integrated bracelet is designed as a seamless continuation of the watch case rather than attaching with traditional lugs and spring bars. The first links are shaped to flow directly from the case, creating a unified design.

In-House Movement

An in-house movement is a watch movement designed and manufactured by the brand itself rather than sourced from an external supplier. Brands often highlight this to demonstrate technical capability and independence.

J

Jewels

Jewels are small synthetic ruby bearings used inside a watch movement to reduce friction between moving parts. They support rotating pivots in the gear train and escapement, helping improve durability and long-term accuracy.

Jumping Hours

Jumping hours is a time display where the hour changes instantly at the top of the hour rather than moving gradually around the dial. The hour is usually shown through a small window while the minutes are indicated separately.

Jewelled Movement

A jewelled movement is a watch movement that uses synthetic ruby bearings at key friction points. The number of jewels is often listed on the dial or movement to indicate how many such bearings are used.

L

LCD (Liquid Crystal Display)

LCD stands for liquid crystal display, a type of digital screen used in many quartz watches. It displays numbers or symbols electronically, often showing the time, date, alarms, or other functions.

Lollipop Seconds Hand

A lollipop seconds hand has a circular luminous marker near the tip. This design is commonly used on dive watches to improve the visibility of the running seconds indicator.

Lugs

Lugs are the projections extending from the top and bottom of the watch case. They hold the strap or bracelet in place using spring bars.

Lug Width

Lug width refers to the distance between the inner edges of the lugs where the strap or bracelet attaches. It is usually measured in millimetres and determines which strap sizes will fit the watch.

Lume

Lume refers to the luminous material applied to hands, indices, or bezels so they remain visible in low light. Earlier watches used radioactive materials such as radium and tritium, while modern watches typically use safer photoluminescent compounds.

Luminova

Luminova is a non-radioactive luminous compound used on watch dials and hands. It absorbs light and releases it slowly in darkness, producing a visible glow.

Luminescence

Luminescence describes the ability of a material to emit light after absorbing energy from another source, such as sunlight or artificial light. In watches, this effect allows hands and markers to glow in the dark.

M

Main Plate

The main plate is the base structure of a watch movement. Most of the movement’s components are mounted on it, with bridges and other plates securing parts above it.

Mainspring

The mainspring is a tightly coiled strip of metal that stores energy in a mechanical watch. When wound, it gradually releases this energy to power the movement.

Manual (Hand-Wound Movement)

A manual movement is a mechanical movement that must be wound by turning the crown. This action tightens the mainspring and provides the energy needed for the watch to run.

Marine Chronometer

Marine chronometers were highly accurate clocks developed for navigation at sea. Their precision allowed sailors to determine longitude, making them essential instruments during the age of maritime exploration.

Mechanical

A mechanical watch uses a system of springs, gears, and an escapement to measure time. Unlike quartz watches, it operates entirely through mechanical components without electronics.

Micro-Rotor

A micro-rotor is a smaller version of the rotor used in automatic watches. It is integrated into the movement rather than sitting above it, allowing the movement to remain thinner.

Mineral Crystal

Mineral crystal is a hardened glass used to protect the watch dial. It is more scratch-resistant than acrylic but softer and less resistant to scratching than sapphire crystal.

Minute Repeater

A minute repeater is a complex striking complication that chimes the time on demand. When activated, it sounds the hours, the quarters, and the number of minutes past the last quarter using small hammers and gongs.

Moonphase

A moonphase complication displays the current phase of the moon as it appears in the lunar cycle, typically using a rotating disc visible through an opening on the dial.

Movement

The movement is the internal mechanism that powers a watch and drives its functions. It includes components such as the mainspring, gear train, and escapement that work together to measure time.

O

O-Ring

An O-ring is a circular sealing gasket, usually made from rubber or synthetic materials, used to keep a watch case water-resistant. It sits between components such as the caseback, crown, or crystal and forms a tight seal when compressed.

Open-Heart Dial

An open-heart dial features a small cut-out in the dial that reveals the oscillating balance wheel of a mechanical movement. It allows the wearer to see part of the movement in operation while the rest remains covered.

Overcoil

An overcoil is a hairspring design where the outer coil curves upward and inward toward the center of the spring. This shape helps the hairspring expand and contract more evenly, improving timekeeping stability.

Oscillation

Oscillation refers to the back-and-forth motion of the balance wheel in a mechanical watch. This repeated movement regulates how the escapement releases energy through the movement.

P

Pallet Fork

The pallet fork is a key part of the escapement that sits between the escape wheel and the balance wheel. It locks and releases the escape wheel in small steps, allowing energy from the mainspring to pass through the movement in controlled intervals.

Panda Dial

A panda dial describes a watch dial with a light-colored background and darker chronograph sub-dials. The opposite combination is often called a reverse panda dial.

Patina

Patina refers to the natural aging that occurs on watch dials, hands, or cases over time. Changes in color or surface texture often develop as materials react to light, moisture, and environmental exposure. Collectors sometimes value patina because it reflects the watch’s age and originality.

Perlage

Perlage is a decorative finishing technique made up of overlapping circular patterns applied to metal surfaces. It is often found on movement plates and inside the case, adding texture and visual detail.

Perpetual Calendar

A perpetual calendar is a highly complex complication that automatically tracks the date, day, month, and leap years. Because it accounts for the varying lengths of months and leap years, it normally does not require manual adjustment until the year 2100.

Pin Buckle

A pin buckle is a simple fastening mechanism commonly used on leather or rubber straps. A small metal pin passes through holes in the strap to secure the watch to the wrist.

Pinion

A pinion is a small gear used in a gear train, usually paired with a larger wheel. It helps transfer motion and control the speed of rotation between components.

Polished

Polished describes a highly refined surface finish that reflects light like a mirror. This finish is often applied to watch cases, bezels, and hands to create a bright, reflective appearance.

Power Reserve

Power reserve refers to the amount of time a mechanical watch can run after being fully wound. Some watches include a power reserve indicator on the dial that shows how much stored energy remains.

Pushers

Pushers are buttons on the side of the watch case used to control functions such as a chronograph. They are usually located next to the crown and activate start, stop, or reset functions.

PVD (Physical Vapour Deposition)

PVD is a coating process used to apply a thin, durable layer of color to metal surfaces. It is commonly used to produce black or colored watch cases and bracelets.

Pilot Watch

A pilot watch is designed with aviation use in mind. These watches typically feature highly legible dials, large crowns for easy operation, and clear minute markings for precise time reading.

Q

Quarter Repeater

A quarter repeater is a striking complication that chimes the time on demand. When activated, it sounds the hours first and then the number of fifteen-minute intervals that have passed since the hour using small hammers striking internal gongs.

Quartz

Quartz refers to a type of watch movement that uses a quartz crystal to regulate time. When electricity from a battery passes through the crystal, it vibrates at a precise frequency, allowing the watch to keep highly accurate time.

Quartz Movement

A quartz movement is powered by a battery and regulated by a vibrating quartz crystal. These movements are known for their accuracy, low maintenance requirements, and relatively simple construction compared with mechanical movements.

Quickset Date

Quickset date is a feature that allows the date to be adjusted directly through the crown. This makes it possible to change the date quickly without turning the hands through full twenty-four-hour cycles.

R

Radium

Radium is a radioactive material that was historically used in luminous paint on watch dials and hands. Because of its health risks, it was eventually replaced by safer alternatives such as tritium and modern non-radioactive luminous compounds.

Rattrapante

A rattrapante, also known as a split-seconds chronograph, uses two chronograph seconds hands mounted on the same axis. One hand can be stopped to record an intermediate time while the other continues running.

Regatta Timer

A regatta timer is a complication designed for yacht racing. It typically counts down the minutes leading up to the start of a race, helping sailors time their approach to the starting line.

Regulation

Regulation refers to the process of adjusting a watch movement to improve its accuracy. This usually involves fine adjustments to the balance or hairspring to control the rate at which the watch gains or loses time.

Rehaut

The rehaut is the inner ring between the dial and the crystal. It often carries minute markers or other engravings and helps frame the dial.

Repeater

A repeater is a striking complication that chimes the time when activated. Small hammers inside the watch strike gongs to sound the hours and, depending on the design, minutes or other intervals.

Retrograde

Retrograde refers to a display where a hand moves along a straight or curved scale and then instantly snaps back to the starting position once it reaches the end of the scale.

Rotor

The rotor is the rotating weight used in automatic watches to wind the mainspring. As the wearer moves their wrist, the rotor spins and transfers energy to the winding system.

Rubies

Rubies are synthetic jewel bearings used within watch movements to reduce friction and wear between moving parts. They support pivots in areas such as the gear train and escapement.

S

Sand-Blasting

Sand-blasting is a finishing technique that produces a matte surface by directing fine abrasive particles at metal under pressure. The process removes shine and leaves a uniform, slightly textured appearance.

Sapphire Crystal

Sapphire crystal is a synthetic sapphire material used to protect the watch dial. It is extremely hard and highly resistant to scratches, making it the most common crystal material used in modern watches. Sapphire ranks close to diamond on the hardness scale, though it can still shatter under a strong impact.

Screw-Down Crown

A screw-down crown uses a threaded system that allows the crown to be screwed tightly into the watch case. This compresses internal gaskets and improves water resistance by creating a stronger seal.

Shock Resistance

Shock resistance refers to protective systems built into a watch movement to reduce damage from impacts. These systems typically use small spring-mounted jewel settings that allow the balance wheel pivots to move slightly during sudden shocks.

Sidereal Time

Sidereal time is a method of timekeeping used in astronomy based on the Earth's rotation relative to distant stars rather than the sun. Watches with this complication allow astronomers to track the position of celestial objects.

Skeleton Watch

A skeleton watch features a movement that has been extensively cut away to expose its internal components. This design allows the wearer to see the gears, bridges, and escapement through the dial and caseback.

Solar Power

Solar-powered watches use photovoltaic cells to convert light into electrical energy. This energy is stored in a rechargeable cell that powers the quartz movement.

Spring Bars

Spring bars are small spring-loaded metal bars used to attach a strap or bracelet to a watch case. They fit between the lugs and compress slightly to allow the strap to be installed or removed.

Stem

The stem is the metal shaft that connects the crown to the movement. Turning the crown rotates the stem, allowing the wearer to wind the watch or set the time and date.

Strap

A strap is the band that secures the watch to the wrist. Straps are typically made from materials such as leather, rubber, fabric, or synthetic materials.

Sub-Dial

A sub-dial is a smaller dial placed within the main watch dial. Sub-dials are often used to display additional information such as chronograph timing or a second time zone.

Super-Complication

A super-complication refers to a watch that contains multiple advanced complications, often combining features such as perpetual calendars, repeaters, chronographs, and astronomical displays.

Super-LumiNova

Super-LumiNova is a non-radioactive luminous material used on watch hands, indices, and bezels. It absorbs light and gradually releases it in darkness to improve readability.

Sweeping Seconds

Sweeping seconds describes the smooth motion of the seconds hand on most mechanical watches. Because the balance wheel oscillates several times per second, the hand appears to move continuously rather than ticking once per second.

Synthetic Sapphire

Synthetic sapphire is an extremely hard and scratch-resistant material commonly used for watch crystals. It offers far greater scratch resistance than mineral glass or acrylic.

T

T < 25

“T < 25” is a marking sometimes found on older watch dials indicating the use of tritium-based luminous material. The marking confirms that the amount of radioactive tritium used is below the legal safety limit of 25 millicuries.

Tachymeter

A tachymeter is a scale typically printed around the edge of a chronograph dial or bezel. When used with the chronograph seconds hand, it allows the wearer to calculate speed over a known distance, such as kilometres or miles per hour.

Time Zone

A time zone is a geographic region that follows a standard time used for civil timekeeping. Watches with additional time zone functions allow the wearer to track time in more than one region simultaneously.

Tonneau Case

A tonneau case is a watch case shape with curved sides and a barrel-like form. The design sits between a rectangular and oval profile.

Tourbillon

A tourbillon is a mechanical complication that places the escapement inside a rotating cage. The mechanism was designed to counteract the effects of gravity on the movement’s accuracy by continually changing the escapement’s position.

Tritium

Tritium is a mildly radioactive material that was widely used in luminous paint on watch dials and hands during the mid-20th century. It has largely been replaced by non-radioactive luminous compounds.

Twenty-Four Hour Display

A twenty-four hour display shows the full day on a single scale running from 1 to 24 hours rather than the standard 12-hour cycle. This format is often used on GMT watches and in military timekeeping.

Timing Bezel

A timing bezel is a rotating bezel marked with minute intervals. It allows the wearer to measure elapsed time by aligning the bezel marker with the minute hand.

U

UTC (Coordinated Universal Time)

UTC is the global time standard used for civil timekeeping around the world. It is based on highly precise atomic clocks and serves as the reference from which all time zones are calculated.

V

Vibrations

In mechanical watches, vibrations refer to the back-and-forth movements of the balance wheel as it oscillates. Each swing in one direction counts as a vibration and forms part of the rhythm that regulates the watch’s timekeeping.

VPH (Vibrations Per Hour)

VPH measures how many vibrations the balance wheel completes in one hour. Common mechanical watch frequencies include 18,000, 21,600, 28,800, and 36,000 vibrations per hour.

Variable Inertia Balance

A variable inertia balance is a type of balance wheel that adjusts its rate by altering the distribution of weight on the wheel rather than changing the length of the hairspring. Small adjustable weights on the balance allow watchmakers to fine-tune accuracy.

W

Water Resistance

Water resistance indicates how well a watch case is sealed against water entering the movement. Ratings are usually expressed either in metres or atmospheres (ATM), which represent the pressure the watch can withstand under controlled testing conditions.

ATM Rating

Feet

Metres

Typical Use

1 ATM

33 ft

10 m

Splash resistant. Suitable for accidental exposure to water such as rain or hand washing.

3 ATM

100 ft

30 m

Can handle light splashes or brief contact with water, but not suitable for swimming.

5 ATM

165 ft

50 m

Generally suitable for swimming in shallow water.

10 ATM

330 ft

100 m

Suitable for swimming, snorkelling, and general water sports.

15 ATM

500 ft

150 m

Suitable for swimming, snorkelling, and more active water use.

30 ATM+

1000 ft+

300 m+

Designed for serious water activities such as free diving or scuba diving.

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Winding

Winding refers to the process of tightening the mainspring to store energy that powers a mechanical watch. This can be done manually by turning the crown or automatically through the movement of the wrist in an automatic watch.

Winding Crown

The winding crown is the external knob used to wind the mainspring and adjust functions such as the time or date. It is connected to the movement by the stem.

Winding Stem

The winding stem is the metal shaft that connects the crown to the movement. Rotating or pulling the crown moves the stem, allowing the wearer to wind the watch or set the time.

Z

Zulu Time

Zulu Time is another name for Greenwich Mean Time (GMT) or Coordinated Universal Time (UTC). The term comes from the NATO phonetic alphabet, where the letter Z is pronounced “Zulu,” and it is widely used in aviation and military communication to avoid confusion between time zones.

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