Watch Terms Explained: Part 1 - A to M

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There are literally hundreds of watch terms and finding all the meanings can be hard to here is the first part of watch parts explained letters A - M.

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Analog Display

The time display is shown by hands and a dial, he opposite to digital display.


The water pressure rating of a watch. ATM means atmosphere and is equal to 10 meters of depth. 1 meter is 3 feet, 1 ATM is 10 meters, 5 ATM is 50 meters

Automatic watch

A watch that has the mainspring wound by the movement of the wearer's wrist rather than winding a stem. Also referred to as a 'self-winding' watch. A weight, the rotor, is turned by the motion of the wrist thus winding the mainspring. The energy generated by the movement of the rotor is transferred into the mechanical energy of a spring and then to the watch movement. If an automatic watch winds down most of them can by wound by hand or shaken to get it started again. The system was invented for pocket watches in Switzerland in the 18th Century by Abraham-Louis Perrelet. This system was successfully adapted to the wristwatch in 1923 by John Harwood, an English watchmaker


The ring around the crystal on the top portion of a watch. Usually made of metals such as gold, gold-plate, platinum or stainless steel. Holds the glass or crystal in place.

Bi-directional Rotating Bezel

A bezel that can be moved either clockwise or counter-clockwise. Used to make mathematical calculations or keeping track of elapsed time.


A metal link watch band

Bubble Back

Term given to the case back of the first style automatic watches by Rolex due to it's bubble-shaped screwed case back.

Butterfly Clasp

2 ends of the buckle on a bracelet fold over into the centre. On a deployant clasp one end folds over the full length.

Calendar watches

Have subdials or pointers indicating the month, date and sometimes day of the week.

Simple Calendar - shows the Date of the month only

Day-Date Calendar - shows the Date and the Day of the week

Complete Calendar - shows the Date, Day of the week and the Month


1 carat equals 1-24 of fine gold. 18 carat gold contains 18-24 fine gold or 75% gold content.


The container that protects the watch movement. It also gives the watch an attractive appearance. Cases come in many shapes, round, square, oval, rectangular. A case is called 'shaped' when it is not round. Cases can be made of different metals including stainless steel, gold, titanium, silver and platinum.


The underside of a watch that lies against the skin. Some casebacks are made of crystal allowing you to view the watch movement.


Watches with a built-in stopwatch function. There are 2 independent time systems. One indicates the time of day and the other measures intervals of time. Subdials are used to keep track of seconds and of elapsed minutes and hours. Counters can be started and stopped as desired.


An instrument for measuring time very accurately. For a Swiss watch to be called a chronometer it must meet very high standards set by the C.O.S.C., Controle Officiel Suisse des Chronometres. The requirements are 15 days and nights at 5 different positions and temperature changes.
The Organization of Swiss Watch Manufacturers definition as of 1951: 'A Chronometer is a precision watch which is regulated in various positions and at different temperatures and has received a certificate to that effect'.


The hour and minute hands move around the same axis.


Functions in addition to telling the time of day. Examples of a complication are a chronograph, a power reserve indicator, an alarm and a phase of the moon indicator.


Also called a stem. A knob on the outside of the watch case used to wind the mainspring in mechanical watches. Also used to set the time, when pulled out, and for setting a watch calendar, if fitted. A screw down crown is used to make the watch more water resistant and to help keep out dust.


A transparent cover that protects the watch face. Crystals are made of glass, plastic or synthetic sapphire. Non-reflective coating on some crystals prevents glare.

Plastic Crystals

Acrylic, soft and flexible so they resist small impacts.Surface scratches can be buffed out.

Mineral Crystals

Heat-hardened glass about 10 times harder than plastic. Extremely scratch resistant but must be replaced if they do scratch.

Sapphire Crystals

2 - 3 times harder than mineral glass and virtually scratchproof. They are quite brittle so are more likely to crack or shatter than mineral. Replacement cost is substantially higher than for mineral crystals.

Date Display

Display of date on the dial of a watch.

Day/Date watch

A watch that indicates the day of the week as well as the date.

Deployant Buckle

A buckle that fastens to the watch strap and opens and fastens using hinged extenders. Invented by Louis Cartier in 1910. A deployant buckle is easier to put on and remove than a strap. Deployant comes from the verb 'deployer' which means to unfold. Sometimes mistakenly referred to as a 'deployment' clasp.


The face of the watch showing the hours, minutes and sometimes seconds.

Digital Display

Time is shown by using digits, numbers, instead of hands and a dial.

Display Back

A caseback that is transparent so that the movement may be viewed.


The most important part of the watch. Converts the energy of the mainspring into equal units of time. The escapement allows the power stored in the mainspring to be released in a controlled manner. The regularity is controlled by the balance and it's spring. The escapement controls the rotation of the wheels and thus the motion of the hands. It is fitted at the end of the gear-train and is designed to interrupt the movement of the wheels at regular intervals.


Leading manufacturer in Switzerland for movements used in many Swiss watch brands.

Fly-back hand

In a chronograph there is an additional seconds hand that moves with the seconds hand and can be stopped independently and then made to catch up, 'fly-back', with the other constantly moving seconds hand.


The number of vibrations per hour.


Most water-resistant watches are equipped with gaskets to seal the case-back, crystal and crown from water infiltration. Gaskets should be checked every couple of years to maintain water resistance.


An electro deposited layer of gold. The thickness is measured in microns.

Greenwich Mean Time

The standard for timekeeping that was introduced in England in 1880 and used as the basis for calculating standard time throughout the world. It reflects the mean solar time along the Earth's prime meridian. The prime meridian is 0 longitude. The prime meridian runs through the Greenwich Observatory outside of London, England.


Also called the balance spring. A small spring that is attached to the balance wheel.


The indicator that moves over the dial to point at the hour, minute or second. Watches generally have three hands to show the hours, minutes and seconds. Hands can have very different shapes: pear, Breguet, sword, skeleton, baton, arrow, etc.

Helium Escape Valve

Prior to surfacing from great depths in a pressurized enclosure, such as a diving bell, toxic gases that have been formed in the enclosure are removed and helium is mixed into the air. The helium molecules are lighter than air and can therefore penetrate the watch. When the pressurized enclosure surfaces and is depressurized the helium rushes out of the watch so quickly that the glass on the watch pops out as well. The watch was built to withstand external pressure, not internal pressure. The glass popping out can be avoided by opening the Helium Escape Valve on the watch during resurfacing, which allows the helium to escape but prevents water from entering the watch.

Horns or Lugs

Projections on the watch case. There is a spring bar between the 2 horns that is used to fix the strap or bracelet.


The science of the measurement of time.

Hour Markers

Arabic numerals, Roman numerals or symbols placed around the dial to mark the hours.


A shock-proofing system for mechanical watches in use since 1933. It is the best known shock absorber for watches.


Bearings that are used in a watch movement to reduce friction. They are usually synthetic sapphires or rubies. They help to maintain the watch's lubrication with far less friction than metal.


A quartz movement that does not use a battery. Energy is stored for a period of time through movement of the wrist that charges a capacitor.


Light Emitting Diode. Used in digital displays on electronic quartz watches.

Limited Edition

A watch style that has a limited number manufactured. The production of a watch may be limited to 25 or 100 or 1,000 or whatever number the manufacturer decides to use. Each watch is usually engraved showing in what sequence it was made. e.g. 42-100 would be the 42nd watch made out of a total production of 100.

Liquid Crystal display

The time is displayed electronically by using a thin layer of liquid held between 2 plates, the top plate being transparent.


To emit rays of light. A luminescent material is deposited on numbers and hands in order to read the time in the dark.

Main Plate

The base plate on which all the other parts of a watch movement are mounted.


The driving flat-coiled spring of a watch or clock, contained in the barrel. Supplies power to the watch.


A watch movement that must be wound manually every day or two to keep it running.

Mechanical watch

Origin dates back to the 14th century. It is made up of about 130 parts assembled in the three main parts which are: 1. the source of energy, 2. the regulating parts, 3. the display.
The number of component parts is much higher in so-called complicated watches, date, phases of moon, fly-back hand, etc. The 'Ebauche', about 60 parts, fitted with the regulating and certain other parts, forms the movement, in other words the internal mechanism of the watch, which makes it possible to maintain a constant tension in the spring once it has been wound manually or automatically, by movements of the wrist, and to regulate the display by means of the hands, hours, minutes, seconds.

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