Watch Know-how - A brief guide

Analogue watch
In watch terms, analogue is a watch that shows the time using hands, as opposite to a digital watch that shows the time in numbers on a LCD-screen.

Alarm
A watch with an alarm function enables the user to set reminders with either visual or audial signal.

Anti-reflex coating
The glass of most watches is coated with anti-reflex film, enabling you to tell the time without glare cuased by, for example, direct sunlight.

ATM
ATM is short for atmospherical preassure, and is used to designate water-resistance. One ATM is approximatley equal to 10 Meters. For a watch to be considered waterproof from swimming, a minimum of 10 ATM / 100 M resistance is advised. For diving, at least 20-30 ATM is recommended.

Arabic numerals
The numbers now used in the western world were introduced to us in medieval times by arabic merchants. Hence they are called arabic numerals( 0, 1, 2, 3, 4, 5, 6, 7, 8, 9).

Back casing
The back casing is the rear of the watch, usually comes as either screw-down or preassure type. The back casing on high-end watches is often decorated and in some cases transparent to reveal the movement of the watch.

Battery
See quartz.

Battery indicator
A battery indicator shows the amount of power left in the battery and thus enables the wearer to tell when it's running out and needs to be changed.

Case
The case of the watch is the outer shell containing the watch movement. It is usually made in steel, gold, titanium or ceramic material.

Tang-type buckle
A tang-type buckle is reminiscent of the closing mechanism of a belt. The tang type buckle is used on leather or rubber watch straps.

Diameter
The diameter of a watch is meassured across the outside of the watch casing and does not include the size of the crown or push-buttons.

Perpetual calendar
A perpetual calendar is a highly complex and quite rare function on a watch - it shows the date and takes into account the varying lenght of the months and, in extremely rare occurances, also leap years and the non-occurance of the actual leap day every 100 years.

Happy watch
When an analogue watch is ten-past-ten or ten-to-two, the hands are in a "smiling" position. When photographing a watch for marketing purposes the hands are usually in either of these positions.

Glass
The glass of a wrist-watch is usually one of two types: sapphire or mineral. Sapphire is most common as it offers a very good resistance to scrathes from everyday wear. Mineral glass, while being softer and more easily scratched, has the advantage in that if it breaks it does not shatter into sharp pieces. Mineral is therefore used in applications where sharp glass shards would cause hazard, for example all watches used by NASA must have mineral glass.

GMT
GMT, Greenwich Mean Time, is the timezone used to coordinate UTC (Coordinated Universal Time). UTC is the base for all civilian time-keeping standards and is kept by atomic watches with extreme precision. In watch terms, GMT is the name for a function that allows the watch to show two different time zones.

Guilloche
Guilloche is a type of decoration normally used on watch dials. A proper guilloche pattern is made by cutting into the surface by means of a very expensive and time-consuming engineering process. Nowadays, most watch companies stamp the pattern instead of cutting it, one of the few exceptions is Breguet who still perform the proper guilloche cutting.

Power reserve
The power reserve is what keeps the watch ticking once it has been wound. Some mechanical watches have a power reserve indicator to show the amount of power remaining. For battery operated quartz watches, the power reserve is typically meassured in years rather than days, as is the case with mechanical watches.

Hesalite
A type of mineral composite glass used by Omega in some models, most famously the Speedmaster "Moonwatch". As other mineral glasses, Hesalite does not shatter into sharp pieces if broken, which is why it's prefered by NASA.

Lug
The four pieces protruding from the watch case where it attaches to the wrist band are called lugs. The width between two lugs (lug width), usually 18-26 mm, is used to determine what size bracelet works with the watch.

Thickness
The thickness of a watch is meassured between the front and rear sides of the casing at its maximum distance.

Index markers
Hour markerings on a watch dial are called index markers. They are usually shaped like lines, dots, arabic numerals, roman numerals or are set in gemstones.

Jewels
To minimize friction and increase the accuracy of a watch movement, jewels are used as bearings between the cogs. These jewels are manufactured in the same way as a sapphire glass, the number of jewels is used to indicate the complexity of a watch movement. The higher the number of jewels, the more complex the movement.

Calibre
Calibre is another name for the watch movement. An advanced calibre may be used for several functions such as chronograph, perpetual calendar and minute repeater. The quality of the caliber also affects the maximum possible power reserve.

Ceramic
Ceramic materials are increasingly popular in watch making. It is very hard, harder than steel, and also better in retaining its original color without being faded by UV-lighting.

Complication
Any function, such as chronograph, date-indication, alarm etc., in a watch movement is called a complication. A watch with a large number of complications is called "Grande Complication".

Crown
The crown is the button used for setting the time and, if applicable, date on a watch. It may be screwed down to increase water resistance and is most commonly situated at the 3 o'clock position.

Chronograph
Chronograph is a complication that enables the user to meassure time intervals.

Chronometer
Chronometer is a title given to a watch which has passed the rigorous testing of C.O.S.C., an independent Swiss quality insurance institute. The original purpose of this test was to certify that a watch was accurate enough to be used for navigational purposes, where the life or death of many people may well hinge on an accurate reading.

Mechanical watches
Each individual watch is tested in five different positions in three different temperatures, over a period of sixteen days. A mechanical watch must not deviate more than -4/+6 seconds/day to pass the C.O.S.C. test.

Quartz watches
Each individual watch is tested in one position in three different temperatures, over a period of eleven days. To receive the C.O.S.C. certificate the watch must be ten times as accurate as a standard quartz watch and must not deviate more than 0,2 seconds per day in any direction.


Quartz
Quartz is a type of crystal used for time-keeping. It is vibrated by an electronichal conductor and the number of vibrations are used to meassure the time. Today, synthetic crystals are used and cut for optimal performance, enabling very exact timekeeping.

Limited edition
Some watches are produced in limited editions, usually these are specialized in apperance or function and are often made to commemorate anniversaries of a certain series or such.

Automatic, self-winding
An automatic or self-winding watch is powered by a mainspring, which is wound up by an attached rotor weight that spins when you move your wrist.

Hand-wound, mechanical
A mechanical watch where the main spring is wound manually by twisting the crown.

Minute repeater
A Minute repeater is a complex, highly valued and often quite expensive complication in mechanical watches. It's an ingenious function that tells the time using at least two differently tuned chimes to mark the hours, quarter hours and minutes at the press of a button. Certain models may also be programmed to sound an alarm at a pre-set time.

Moon phase
A complication showing the different phases of the moon on the dial.

PVD
PVD (Physical Vapour Deposition) is a way of coating metal with a harderning substance. It provides a very durable, low friction surface. PVD-coatings are usually black or dark grey and is usually made to steel or titanium watches.

MOP
MOP is short for Mother of Pearl which is an organic composite material sometimes used in watch dials. Its shiny and complex surface makes it very attractive, it's commonly used in jewellery-like ladies watches but can also be found in certain Rolex mens models.

Rattrapante
Rattrapante is an advanced chronograph complication where two different seconds hands move independently of each other. This enables trackng of multiple time intervals.

Ring
The ring, also known as the bezel, holds the glass in position on a watch. If it's a divers watch, it may be turned so as to indicate elapsed time during a dive.

Roman numerals
Used on the dial as an alternative to arabic numerals for time indication, using the method of counting invented by the old Romans. The Roman numerals for 1-12 are I, II, III, IIII, V, VI, VII, VIII, IX, X, XI, XII.

Skeleton Dial
Skeleton dials are a great tradition in watch-decoration and are guranteed eye-catchers. A skeleton dial is partly or fully cut-away to reveal the very heart of the watch, the inner workings of the movement which is often intricately decorated.

Screw-down crown
A screw-down crown is used on divers watches to secure the crown and prevent water from entering the watch case even when diving at great depths.

Safety valve, helium
A valve used to let helium escape from a divers watch, to prevent over-preassure from building up and exploding the glass of the watch. May be automatic or manual.

Tachometer
A tachometer is a scale placed around the bezel or the edge of the watch dial to allow the user to calculate speed using the chronograph function and a reference distance.

Tritium
Tritium is a weakly radioactive isotope of hydrogen, used in watch making for its illuminating qualities - it glows in the dark! The radioactivity is too weak to be considered harmful to humans, but all watches using tritium must indicate this with a T on the dial, usually placed near the 6 o'clock index marker.

Tourbillon
The Tourbillon was invented by master watchmaker Louis Breguet in 1801. It used a rotating platform to compensate for minor disturbances in watch accuracy caused by earth's gravitation. It is a highly regarderd and sough after complication, usually available only on very high-end watches.

Water protection
Some watches are made to be worn under water and are constructed accordingly. These models often have special cases, extra resistant glass, screw-down crowns and some even feature a helium-escape vale, usable when diving only at extreme depths. The screw-down crown was first patented by Rolex on their Oyster-models but has since been implemented by a large number of manufacturers as the crown remains the most sensitive part of any water-protection. It doesn't matter if the watch is certified for diving down to 1000 meters, if the crown is not secured or if the rubber seals are not intact, water WILL enter the watch even at modest depths.