OUR GUIDE TO EVERYTHING YOU NEED TO KNOW ABOUT WATCHES, WRITTEN IN CONCISE YET EXPLANATORY LANGUAGE. IF YOU’RE LOOKING FOR A SPECIFIC DEFINITION, YOU’VE COME TO THE RIGHT PLACE!
A complication in a watch that will make a sound or vibration at a preset time
An essential complication for aviators an altimeter measures altitude, or height above sea level. Recording ascent and descent, an altimeter can also be an important piece of equipment for climbers, walkers, mountaineers and other professionals where altitude is a needed measurement.
A feature that indicates whether the indicated time is AM or PM. This feature can be found mostly (although not limited to) in watches with a GMT/Dual time display or a World Time Display to help know whether it is day or night in the other time zones.
Analog/Digital (Duo) Display
A dial or face of a watch that has the ability to display the time using rotating hands or other markers on a dial, (an analog display) and electronically by digital units (a digital display) on the dial simultaneously. This is also known as duo display or an AnaDigi watch.
A watch that uses rotating hands or other markers on a dial to tell the time
A complication showing the date, day and month. An extremely complicated and sought after movement. This watch will correctly adjust for short and long months; however, it will not correctly account for Leap Year, the 28 days of February once every four years.
The opening or window found on watch dials in which certain indications are given such as the date window on a Rolex Datejust
Auto Repeat Countdown Timer
A countdown timer that resets itself as soon as the preset time has elapsed and repeats / starts again. The countdown cycle runs continuously until the stop button is pushed.
Automatic Winding Movement
A mechanical watch that uses as its power source the addition of a weighted pendulum called a “Rotor”. The Rotor is attached to the movement, when the watch is in motion and continually worn, the natural motions of the body spin the rotor around the inside of the watch & “automatically” wind or power the movement. If worn every day an Automatic watch will not have to be wound. An automatic watch can and should be wound manually if the watch has stopped or is at the end of its power reserve due to non-wear. To restore the power reserve to an automatic watch simply wind 30-40 times. You can not over wind an automatic watch. Manually winding an automatic watch after the power reserve has depleted or the watch has stopped ensures the watch is at full power reserve. A typical power reserve for an automatic watch is generally 35-45 hours. Consult your manual for specifics.
Also known as the Hairspring, it a very fine spring in a mechanical watch that causes the recoil of the balance wheel. The length and adjustment of its length regulate the watch’s timekeeping.
A separate bridge holding the balance and regulator assemblies.
Analogous to the pendulum in grandfather clocks it is a weighted wheel in a mechanical movement that rotates back and forth separating time into beats. It is a key mechanism producing accuracy of time in a watch.
A cylindrical covered box with gear teeth on the outside that houses the Mainspring in a mechanical watch. The size of the barrel controls the length of the Power Reserve or stored power of a mechanical movement. The teeth surrounding the barrel drive the wheel train.
A ring on the top side of the case surrounding the crystal. It may be decorative or functional. The Bezel can be fixed, move only one way, Uni-Directional, or move both ways, Bi-Directional. Many functional Bezels are useful to calibrate time from any given point by rotating the Bezels 12 position to any given starting point of reference along the dial.
Bi-Directional Rotating Bezel
A bezel that can be moved both clockwise and counter-clockwise to perform mathematical functions using the dial of the timepiece as reference. A bi-directional bezel is similar to a slide rule and is extremely useful for aviators and aviator timepieces.
The metal strap often containing links that attaches to the case of the watch and allows the timepiece to be worn on the wrist.
The spiral hairspring on which the balance swings tends to bunch on opposite sides as it expands or contracts. The constant shift in their gravity disturbs the rate of balance, and Breguet solved the problem in 1795 by upraising the last coil of the spring and giving it a smaller curve. This Breguet overcoil encouraged the spring to develop concentrically, improving the rate of the watch and reducing the wear on the balance pivots.
A metal movement part that is attached to a bottom plate and holds at least one bearing of a rotating part.
A feature that shows the date, and often the day of the week. There are several types of calendar watches. Most calendar watches show the information digitally through an aperture on the watch face. Some chronograph watches shoe the information on sub-dials on the watch face.
This refers to a Domed/Arched Crystal
Caliber or Calibre
Since the early 18th Century, the calibre of a movement has denoted the position and size of its different components, notably the wheel train and the barrel. Today In watchmaking, the term refers to the specific layout and shape of a movement and the bridges, and its various components as well as the designer of the movement.
The container housing the movement of the watch and protecting it against dust, moisture, jarring and other hazards. Usually consisting of the case band, the bezel, and the case back.
Watch or other apparatus with two independent time systems: one indicates the time of day, and the other measures (stopwatch function) brief intervals of time. Counters registering seconds, minutes and even hours can be started and stopped as desired. It is, therefore, possible to measure the exact duration of 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 sub-dials to time elapsed hours, minutes and seconds. Still, others show elapsed time on a digital display on the watch face. Some chronographs can be used as a lap timer (see “flyback hand” and “split seconds hand”). The accuracy of the stopwatch function will commonly vary from 1/5th second to 1/100th second depending on the chronograph. Some chronographs will measure elapsed time up to 24 hours. Watches that include the chronograph function are themselves called “chronographs.” 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 (see “tachometer”). 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.
Technically, all watches are chronometers. But for a Swiss made watch to be called a chronometer, it must meet certain very high standards set by the Swiss Official Chronometer Control (C.O.S.C.). If you have a Swiss watch labeled as a chronometer, you can be certain that it has a mechanical movement of the very highest quality– undergone a series of precision tests in an official institute. The requirements are very severe: a few seconds per day in the most unfavorable temperature conditions (for mechanical watches) and positions that are ordinarily encountered.
One or more features added to a watch in addition to its usual time-telling functions, which normally not only include the hours, minutes and seconds but also date and often the day of the week as well. Complications such as; perpetual calendars, moonphase displays, alarms, repeating mechanisms, quarter strikes as well as stop/start chronograph functions. Power reserve indicators are also usually regarded as ‘complications’
Control Officile Suisse de Chronometers or Swiss Controle Officiel des Cronometres- the independent Swiss regulatory organization that rigorously tests and certifies (or fails) watch movements for chronometer status.
A function that lets the wearer keep track of how much of a preset period of time has elapsed. Some countdown timers sound a warning signal a few seconds before the time runs out. These are useful in events such as yacht races, where the sailor must maneuver the boat into position before the start of a race.
The crown often referred to as the winding crown or winder is used for winding the watch in the case of a non-automatic, for setting the hands to the correct time and often for setting the date in the case of calendar equipped watches. On diving/sports models, the crown may be screw-down whereby it screws onto a threaded tube, which protrudes from the case of the watch. This often ensures superior water resistance.
The cover over the watch dial is called the crystal. There are three types of crystals commonly used in watches: acrylic crystal is an inexpensive plastic that allows shallow scratches to be buffed out. Mineral crystal is composed of several elements that are heat-treated to create an unusual hardness that aids in resisting scratches. Sapphire crystal is the most expensive and durable, approximately three times harder than mineral crystals and 20 times harder than acrylic crystals. A non-reflective coating on some sport styles prevents glare.
A watch that shows both the day of the week and the date of the month.
Day/Night or AM/PM Indicator
A feature that indicates whether the indicated time is AM or PM. This feature can be found mostly (although not limited to) in watches with a GMT/Dual time display or a World Time Display to help know whether it is day or night in the other time zones.
Deployment (Foldover) Buckle
A three-folding enclosure that secures the two ends of the bracelet and allows enough room for placing the watch on the wrist when fully deployed. When closed, the buckle covers the two-piece folding mechanism.
A watch that shows the time in numbers, or digits, rather than hands and a dial. Liquid crystal display (LCD) is commonly used.
A watch that shows local time and the time in at least one other time zone. This is generally displayed by an additional hour hand which tracks time in a 24 hour mode. Some watches have a separate sub-dial showing the full clock at the additional Time Zone.
A display that shows the time both by hour and minute hands (an analogue display) and by numbers (a digital display). This is also known as AnaDigi display.
Disc or plate made of metal or another substance, inscribed with various markings, including obvious indications for the hours, minutes and seconds. Uniquely varied in shape, decoration, material, they are inscribed with numerals, figures, symbols, divisions and other information.
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. You can then read the elapsed time off of the bezel. This saves from having to perform the subtraction that would be necessary if you used the watch’s regular dial.
End of Life. In quartz movement, the end of battery life is indicated by the second hand, which starts to jump every four seconds. The battery should be changed immediately.
This is a centuries-old craft that, still today, involves the use of antique machines to engrave delicate patterns on metal watch components, including cases, dials, bezels and movements. It is also known as guilloche.
Equation Of Time or EOT
An Equation Of Time (aka EOT) complication indicates the difference between “true” solar time (that of nature) and “mean” solar time (that of man). As the earth orbits around the Sun in an elliptical (oval) shape & the axis is tilted – there are only 4 days a year when the day is exactly 24 hours long April 15th, June 14th, September 1st and December 24th. All other days of the year the days are shorter or longer – depending on the position of the earth. This watch will show the difference between the “mean” time & the “true” time. Since the number of the days are fixed year after year (at the same location) a watch can be manufactured to replicate the correction via a shaped cam which elongates & shortens the days accordingly.
The device at the heart of virtually all time-keeping mechanisms. The mechanism that “releases” the energy that maintains the oscillations of the balance wheel which governs the rate at which the escapement lets the wheels and hands of the watch revolve.
A seconds hand on a chronograph that can be used to time laps or to determine finishing times for several competitors in a race. Start the chronograph, putting both the flyback hand and the regular chronograph seconds hand in motion. To record a lap time or finishing time, stop the flyback hand. After recording the time, push a button and the hand will “fly back” to catch up with the constantly moving elapsed-time hand. Repeat the process to record as many lap times or finishing times as needed. In chronographs with numerical display, a “function” having the same effect.
Also known as complications. A term used to describe the various different tasks a watch can perform such as chronograph and countdown timer.
The system of gears which transmit power from the mainspring to the escapement.
GMT Time Zone
Greenwich Mean Time (GMT) is also known as Zulu Time and UTC (Universal Time Coordinated). The standard by which all World Time is set was agreed at the 1884 International Meridian Conference at Washington DC, USA. It placed Greenwich on the Prime Meridian (Zero Longitude). Greenwich Mean Time or GMT is the time standard against which all other time zones in the world are referenced. It is the same all year round and is not affected by Summer Time or Daylight Savings Time. GMT was originally set-up to aid naval navigation when the globe started to open up with the discovery of the “New World” (America) in the Fifteenth Century. Generally, when the GMT term is used with watches it refers to the ability of the watch that shows local time and the time in at least one other time zone in a 24-hour mode. The reason for showing the additional time zone in 24 hour mode is to allow the wearer to know if the second time zone is in AM or PM.
An application of gold over the surface of an item. The thickness of the plating is measured in microns (1000th of a mm).
Also known as Engine Turning. It is an engraving technique in which a very precise intricate repetitive patterns or design is mechanically etched into an underlying material with very fine detail. Specifically, it involves a technique of engine turning, called guilloche in French, after the French engineer “Guillot”, who invented the machine that could scratch fine patterns and designs on metallic surfaces.
Also known as a balance spring. A very fine spring in a mechanical watch that causes the recoil of the balance wheel. The length and adjustment of its length regulate the watch’s timekeeping.
Helium Escape Valve
A feature found on some diving watches. It provides functionality for professional divers operating at great depths for prolonged periods of time or under saturation, breathing Hypoxic trimix or other mixed gases with helium in them. Because helium is such a small molecule (the second smallest there is), over time in a pressurized diving bell, helium will sneak its way past the o-rings into the inside of a dive watch. While at depth this causes no problem, it will as the divers decompress the helium which is unable to escape the watch. With a standard dive watch, this would lead to the watch crystal popping out from internal pressure. To stop this from happening, high-end, professional diver watches have a helium escape valve or helium bleed valve to let out this extra pressure during decompression. This is a one-way valve which allows the helium to escape.
The science of measuring time and technology of constructing instruments for its measurement or recording. Encompassing the art of designing and constructing watches.
Index Hour Marker
A simple stick/line design hour indicator on an analog watch dial, used instead of numerals.
In watchmaking, a synthetic ruby used for making low friction bearing in which the delicate pivots of the movement wheels run in. In some deluxe watches, sometimes sapphires or garnets are used. Expensive watch movements are jeweled from the barrel to the balance, and all automatic work, date and complication movements are expected to bejeweled.
A jump hour indicator takes the place of an hour hand. It shows the hour by means of a numeral in a window on the dial of the watch. The word “jump” refers to the fact that the numerals jump from 1 to 2 to 3, etc., rather than showing intermediate times between hours as hour hands do. The minutes and seconds in a jump hour watch are read as normal from the analog hands and dial.
A chronograph function that lets the wearer time segments of a race. At the end of a lap, the wearer stops the timer, which then returns to zero to begin timing the next lap.
The lever divides into two pallets which lock and unlock the escape wheel teeth. The action is governed by the balance engaging the other end of the lever, the escape teeth sliding on the inclined pallets life the lever to impulse the balance.
Liquid Crystal Display (LCD)
Liquid crystal display (LCD) in digital watch display that shows the time electronically by means of a liquid held in a thin layer between two transparent plates. All LCD watches have quartz movements.
Luminous dials first appeared during the Great War when soldiers needed to tell the time in the dark. Early forms used Zinc Sulphide compound agitated by a radioactive salt. It was painted on hands and was potentially dangerous to those applying it. Its use was banned in the ’50s, since Tritium, a substance with low radioactivity, replaced it. Other methods have been devised. Timex’s ‘Indiglo’ uses electronic luminescence; a button on the side of the case causes a tiny current from the battery to the electrodes and gives off energy in the form of light. Seiko uses fluorescent material on the dial, activated by any exposure to light.
Double extension of the case middle by which a strap or bracelet is attached.
Base plate on which all the other parts of a watch movement are mounted.
The coiled spring which provides the power to drive a mechanical watch movement.
Manual Wind Movement
A mechanical movement in which winding is performed by hand. The motion transmitted from the user’s fingers to the crown is forwarded to the movement through the winding stem to the barrel, through a series of gears to the mainspring.
Arguably the most accurate timepiece in the world, a Marine Chronometer is a mechanical or electronic timekeeper that is enclosed in a box and is used for determining the longitude on board a ship. Marine chronometers with mechanical movements are mounted on gimbals so they are in the horizontal position that is essential for their precision.
A feature that allows the wearer to convert one type of measurement into another. It usually consists of a graduated scale on the bezel or dial.
A movement based on a mainspring which when wound slowly unwinds the spring in an even motion to provide accurate timekeeping. As opposed to a manual mechanical watch which needs to be wound on a consistent basis, an automatic mechanical requires no winding because of the rotor, which winds the mainspring every time you move your wrist (see our section on automatic watch maintenance for more details).
This is a thousandth of a millimeter and is a measurement used for the thickness of gold plating.
A Complication on a watch that can strike the time in hours, quarters, or seconds by means of a push piece on the case. One of the most expensive complications on a mechanical timepiece.
Mono (Single) Pusher Chronograph
A stopwatch operated by a single button. While 99% of chronographs are operated by the use of two button – one to start & stop the stopwatch, the second to reset the stopwatch; a Mono Pusher complication allows for 1 button to start, stop & reset the stop-watch.
An indicator that keeps track of the phases of the moon. A regular rotation of the moon is once around the earth every 29 days, 12 hours and 44 minutes. Once set, the moon phase indicator accurately displays the phase of the moon.
Mother of Pearl
Iridescent milky interior shell of the freshwater 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.
The means by which a watch keeps time, often including the power source. For example, a watch with mechanical movement uses a spinning balance wheel powered by a tightly wound spring, whereas a watch with quartz movement measures the vibrations in a piece of quartz and often is powered by a battery.
Numeral (Roman and Arabic) are used to present information in the dial and subdials
A complication displaying the day of the week, the date, the month & day; also correcting for leap years – and the phases of the moon. Operating on the 400-year cycle, perpetual calendars require no manual correction before February 2100. Perpetual calendars are almost always self-winding and, if worn constantly, are one of the most useful of all complications.
A rare precious metal, platinum also is one of the strongest and heaviest, making it a popular choice for setting gemstones, jewelry, and watches. It has a rich, white luster, and an understated look. Platinum is hypoallergenic and tarnish resistant. Platinum used in jewelry and watches is at least 85 to 95 percent pure. Many platinum watches are produced in limited editions due to the expense and rarity of the metal.
Power Reserve Indicator
Also known as Reserve de Marche, a feature that shows when the mainspring in the watch will need to be wound. This is a complication for mechanical watches that is quite useful and is usually indicated in hours, except in the case of watches that have a very high power reserve numbering in the days.
A scale on a chronograph which is used for measuring pulse rate.
A button that is pressed to work a mechanism. Push-pieces are usually found on chronographs, striking watches, and alarms.
Quartz is a piezoelectric material, meaning that it generates an electrical charge when mechanical pressure is applied. These crystals also vibrate when a voltage from an outside source, such as a battery, is applied. Piezoelectricity was discovered by Pierre Curie and his brother Jacques in 1880. In the early 1920s, W.G. Cady recognized that due to their elastic qualities, mechanical strength and durability, quartz crystals could be used to fabricate very stable resonators. Cady also concluded that the crystal could be cut in specific ways which would create resonators of almost any frequency that were practically independent of temperature variations. Quartz crystals were first used as a time standard by Warren Marrison, who invented the first quartz clock in 1927. Juergen Staudte invented a method for mass-producing quartz crystals for watches in the early 1970s.
A caliber that uses the vibrations of a tiny crystal to maintain timing accuracy. The power comes from a battery that must be replaced about every 2-3 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 (Kinetic & solar-tech).
Rattrapante Aka Split Seconds Chronograph
The addition of a flyback hand (rattrapante) significantly increases the potential uses for chronographs. It makes possible the measurement of split-second times or timing simultaneous events of unequal duration.
Regulator or Regulateur
A Regulator display separates the minute and hour hands onto a separate axial & sub-dial. This allows for accurate time telling at a glance without the chance of having the watch hands covering each other.
Reserve de Marche
Also known as Power Reserve Indicator. A feature that shows when the mainspring in the watch will need to be wound. This is a complication for mechanical watches that is quite useful and is usually indicated in hours, except in the case of watches that have a very high power reserve numbering in the days.
Used to describe a pointer hand on a watch dial (often a subdial), which returns to zero at the end of a prescribed period. For an example, a watch may have a retrograde date – in Used to describe a pointer hand on a watch dial (often a subdial), which returns to zero at the end of a prescribed period. For example a watch may have retrograde date – in this case, the hand moves up a scale a day at a time, pointing to the current date – when it reaches 31 it will spring back to 1 this case the hand moves up a scale a day at a time, pointing to the current date – when it reaches 31 it will spring back to 1.
A bezel (the ring surrounding the watch dial) that can be turned. Different types of rotating bezels perform different timekeeping and mathematical functions.
The part of an automatic (or self-winding) mechanical watch that winds the movement’s mainspring. It is a flat piece of metal, usually shaped like a semicircle, that swivels on a pivot with the motion of the wearer’s arm.
Sapphire crystal is a very hard transparent material commonly used for “scratch-proof” watch glasses. Made by crystallizing aluminum oxide at very high temperatures, it is chemically the same as natural sapphire and ruby, but without the small amounts of other elements such as iron, titanium or chromium that give the gemstones their colors. Sapphire (whether natural or synthetic) is one of the hardest substances, measuring 9 on the Mohs scale, a system for rating the relative scratch hardness of materials. (Diamond measures 10, the highest rating, and the hardest steels are 8).
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.
A resilient bearing which takes up the shocks received by the watch’s balance staff and protects its pivots from damage. As defined by the U.S. government regulation, a watch’s ability to withstand an impact equal to that of being dropped onto a wood floor from a height of three feet.
A watch in which the case and various parts of the movement are of transparent material, enabling the main parts of the watch to be seen.
Slide Rule aka Navigation Computer
A device, consisting of logarithmic or other scales on the outer edge of the watch face, that can be used to do mathematical calculations. One of the scales is marked on a rotating bezel, which can be slid against the stationary scale to make the calculations. Some watches have slide rules that allow specific calculations, such as for fuel consumption by an airplane or fuel weight.
Solar Powered Batteries
Batteries in a quartz watch that are recharged via solar panels on the watch face.
Split Seconds Chronograph Aka Rattrapante
A feature on a chronograph that actually is two hands, one a flyback, the other a regular hand. To time laps or different finishing times, the wearer can stop the fly backhand independently while the regular hand keeps moving.
An extremely durable metal alloy (chromium is a main ingredient) that is virtually immune to rust, discoloration, and corrosion; it can be highly polished, thus resembling a precious metal. Stainless steel is often used even on case backs on watches made of other metals and is the metal of choice used to make high-quality watchcases and bracelets. It is also hypoallergenic because it doesn’t contain nickel.
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”.
The part of a quartz movement that moves the gear train, which in turn moves the watch’s hands.
A precious metal. Sterling refers to silver that is 92.5 percent pure. The silver fineness should be stamped on the metal, sometimes accompanied by the initials of a designer or country of origin as a hallmark. A protective coating may be added to prevent tarnishing.
A small dial used for any of several purposes, such as keeping track of elapsed minutes or hours on a chronograph or indicating the date.
As a part of a move towards greater consumer protection and in order to combat fakes in the Far East that claim to be Swiss made, the Swiss federal council in 1993 laid down the rule that a watch has to satisfy before it could be described as Swiss made. The movement must be of Swiss origin, and must contain at least 50% Swiss parts. The watch must be cased in Switzerland and pass its final inspection in that country.
A certificate of origin – A mark identifying a watch that is assembled in Switzerland with components of Swiss origin
Tachymeter Scale aka Tachometer
A common feature in chronograph watches. Measures the speed over a predefined distance. The wearer starts the chronograph when passing the starting point and stops it when passing the finish. The wearer can read the speed in units per hour off the tachometer scale. The scale is generally engraved on the bezel or printed on the outer diameter of the dial.
A tang buckle is a traditional Loop & Pin (belt type) buckle.
A rectangular watch with bars along the sides of its face. It was inspired by the tracks of tank used in World War II and designed by Louis Cartier.
An instrument used for registering intervals of time (duration, brief times), without any indication of the time of day.
A “space age” metal, often having a silver-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 saltwater corrosion makes it particularly useful in diver’s watches. Since it can be scratched easily, some manufacturers use a patented-coating to resist scratching. Titanium is also hypoallergenic.
A mechanism that keeps track of elapsed time and displays it, usually on a subdial on the watch dial. Same as a “recorder” or “register”. The term “totalizer” can be used more generally to refer to any counter on a watch.
A device, invented by Breguet in 1801, in which the escapement is mounted in a small revolving cage as a means of overcoming the effects of gravity on the precision of a mechanical timepiece. The mechanism that even in its most conventional version, is extremely hard to manufacture and generally demands a high premium.
Uni-Directional Rotating Bezel
An elapsed time rotating bezel (see “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 err 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 Per Hour or VPH
Movement of a pendulum or other oscillating element, limited by two consecutive extreme positions. The balance of a mechanical watch generally makes five or six vibrations per second (i.e. 18,000 or 21,600 per hour), but that of a high-frequency watch may make seven, eight or even ten vibrations per second (i.e. 25,200, 28,800 or 36, 000 per hour).
Describes the level of protection a watch has from water damage. A watch that is water resistant can withstand water to a certain extent. Check the watch manual to find out the exact level of water resistance your watch is.
Operation consisting of tightening the mainspring of a watch. This can be done by hand (by the crown) or automatically (by a rotor, which is caused to swing by the movements of the wearer’s arm).
World Time Complication
A dial, usually on the outer edge of the watch face, which 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.”
Water Resistance Guide
A watch rated as water resistant may come in contact with water to a predetermined extent. Most watches have a measurement until which the depth of immersion is safe. It is important to remember that a water-resistance rating is based on optimum conditions in a laboratory. Real life experience & aging of the gaskets will effectively decrease the manufacturer’s specifications of water resistance over time. The worst scenario possible is that moisture is allowed to make contact with the movement – thus we strongly suggest that you always work well within the parameters of the manufacturer’s recommendations and have your watch tested at least once a year. Any competent watchmaker has the necessary equipment to test water resistance. It is important to remember that all watches have limits and no watches are waterproof.
Optimum water resistance on a watch is obtained by 3 important factors:
1. Case back – this refers to how the case back is attached to the watch.
Snap-on case backs are sealed by pressure and are considered the least water resistant. The slightest nick in the case or a deformity in a gasket (which will happen over time) will allow water to penetrate the case. Generally, these watches will have a water resistance of 30m/99ft maximum – which allows for contact with water, such as washing hands, but not immersion.
Case-backs attached with screws are the second level of water resistance. Having the case back attached with screws allows for a much tighter seal than a snap-on case back, however, a deformity in the gasket will still allow water to penetrate. Generally, these watches will have a water resistance of 100m/330ft maximum – which allows for light immersion such as swimming in a pool.
Screw-down case backs are threaded and screws into the actual case. This creates a double seal, using both the threading & the gasket as a seal coupled with the deep water pressure. Generally, diving watches with water-resistant ratings greater than 100m/330ft will have this type of case back.
2. Crown – the single most important factor to ensuring water resistance.
The weakest link in a watch for water to penetrate is the crown-stem hole. The stem of the crown is attached to the movement through a hole in the case edge. As the crown is constantly moved to different positions, wound and turned to correct the time, the gasket is constantly compressed, chafed & stressed. The slightest variation in the shape of the gasket or if the crown is not pushed all the way in will allow water to penetrate the watch through the stem hole.
Screw-Down crowns are threaded & screwed shut to a matching threaded tube in the case. The crown has a gasket that is compressed & seals the opening when the crown is tightened – thus ensuring water resistance. A screw-down crown is an essential feature for any watch you intend on swimming with. As matter of fact, we do not recommend swimming with a watch that does not have a screw-down crown. No matter if the watch has a screw-down crown & chronograph pushers, the crowns & pushers are never to be pushed, adjusted or operated when the watch is immersed in water – unless otherwise stated by the manufacturer. An additional benefit of the screw-down crown is that the crown is somewhat more protected from accidental knocks.
“O” rings are made of rubber, nylon or Teflon which form watertight seals at the joints where the crystal, case back and crown meet the watch case. If the watch is a chronograph, the chronograph pushers will also have gaskets to protect from dust and dirt, check with your manufacturer if you are unsure as to whether the pushers on your watch can be operated in wet conditions, it’s not a law that chronographs must be operable under water.
Gaskets begin to erode and break down over time, diminishing the water resistance of a watch. It is important to test your watch once a year for water resistance. Any competent watchmaker should have the necessary basic equipment to test the watch – the cost involved should be minimal.
Real Life and Water Resistance
When a watch is tested by the manufacturer it is usually done in a laboratory under optimum conditions, such as a fresh gasket, sitting stationary in a pressured water tank and with still/motionless water. However, real-life action will produce completely different results. Here are a few scenarios:
Water temperatures in a hot tub or a hot shower will effect the shape of the gasket seals. Especially if the watch is taken from hot temperatures & immediately plunged into cold water – such as going from a hot tub into a pool.
Sudden & rapid changes in pressure – such as diving (even shallow diving) into a pool, the force of plunging your arm into the water while swimming, will stress the gaskets for a fraction of a second. If the gaskets are not up to specification they may rupture and cause the watch to take in water.
As the watch ages, the seals begin to erode & will not maintain the same water resistance levels.
Water Resistance vs. Water Proof
The U.S. FTC (Federal Trade Commission) which enforces the truth-of-advertising has deemed the term “Waterproof” inappropriate. In their opinion, a watch can never be 100% truly impervious to water, as the gaskets deteriorate over time & exposure, thus reducing the specified depth of water resistance. In the words of the FTC: “The word proof connotes a measure of absolute protection that unfortunately does not exist with respect to watches, especially over prolonged periods of time.” The FTC has found the term Water Resistant to be more appropriate.
Water Resistance Testing Methods
There are 2 commonly used water-resistance testing methods:
Dry Test – The watch is placed in a chamber and the air pressure is increased. The machine will detect the smallest variation in the case size. If the case expands, even slightly, then the watch is not water resistant.
Wet Test – The watch is placed in a chamber which is half filled with water and half air. Air pressure is increased while the watch is out of the water, then the watch is slowly immersed in the water. Once the watch is completely immersed, the air pressure is slowly released. If bubbles come out of the watch it means that air entered the watch prior to immersion & the watch is not water resistant. This method is generally used as a second test to pinpoint the problem area.
Units of Water Resistance based on pressure
Meters/Feet: This is the most common way of measuring the water resistance of a watch. 100 meters is just over 328 feet.
ATM: This stands for Atmospheric Pressure. At sea level, the ATM rating is 1, which is equal to 10 meters.
Bar: Bar is a metric unit of pressure named from the Greek word Baros which means weight. It isn’t isn’t commonly indicated on a watch because meters/feet and ATM are more widely understood by the general public. 1 bar is equal to 100,000 Pascals, 14.5 PSI (Pounds per Square Inch) or 0.98 ATM.
Helium Escape Valve
The Helium Escape/Relief Valve is used only by deep diving expeditions when a diver operates from a diving bell. As the bell is lowered pressure begins to increases & helium is added to the breathing mix. Oxygen becomes toxic at a higher pressure, for example, pure oxygen would become toxic at 6 meters. Normal air would become toxic at the pressures technical divers and saturation divers usually work at. They usually use a mixture of three gases (Oxygen, Nitrogen and Helium), known as Trimix. Helium makes up a significant proportion of the mixture because it does not have a narcotic effect on the body, therefore reducing the risk of nitrogen narcosis (the bends) from occurring. Not only this, but helium has a lower density than normal air which means that it is also easier to inhale under water.
The problem is that helium is one of the smallest molecules & will seep into the watch through the seals until the air pressure in the watch equals the air pressure in the diving bell. As the diving bell surfaces & decompresses, the helium molecules inside the watch expand, if there isn’t a valve then the pressure in the watch will pop the crystal off. To avoid this, Omega and Rolex developed their own helium escape valve systems which allow the helium to escape. Omega uses a second crown which screws closed on all Seamaster watches except for the Aqua Terra which doesn’t have one and the Ploprof which uses the automatic helium escape valve design that is common on Rolex diving watches. Many brands use the escape valve in one design or another. Generally, the escape valve can be found on watches which have a water resistance rating of 300m or greater.
Interpretation of the Depth Ratings
Although a watch may be rated 30m/99ft water resistant, it does not mean that the watch can be immersed to that depth. The depth rating posted by the manufacturer is theoretical in nature and can only be achieved in a perfectly optimum environment of a laboratory – which is impossible to replicate in real life. It’s also important to consider that watches such as the Rolex Datejust and Datejust II models might well be rated to 100m and therefore great for swimming with, but they were not designed as full-on diving watches and therefore may not survive prolonged experiences of over 50 meters. You should also consider any chemicals that might be in the water and whether they can react to materials used in the construction of the watch.
Water Resistance Guide
No rating (Dustproof/moisture proof) – 30m/99ft
Does not allow contact with water
30m/99ft – 50m/165ft
Allows for contact with water such as washing hands and rain
50m/165ft – 100m/330ft
Allows for light pool swimming and swimming to the bottom of the deep end
100m/330ft – 200m/660ft
Allows for swimming and snorkeling
200m/660ft – 500m/1650ft
Allows for impact water sports such as surfing and scuba diving
Appropriate for technical diving
Obviously, the higher the rating, the more appropriate the watch is for deeper diving.
IMPORTANT: We strongly recommend purchasing a watch with a screw-down crown if you intend on wearing the watch while you are in contact with water.
Have your watch water-tested once a year.
Never open, wind or operate the crown while in water.
Never press the buttons of a chronograph watch while in water – unless otherwise stated by the manufacturer.
Do not subject your watch to extreme temperature changes.
Do not subject your watch to sudden & rapid air-pressure changes.
Do not allow your watch to come into contact with corrosive chemicals, such as abrasive soaps & highly chlorinated water.
Ensure that the crown is always pushed in, and if you have a screw-down crown make sure it is always tightened. Double-check before immersing in water.
What about the bath or a shower?
You must not wear your watch into the washroom if you have a habit of daily washing, even if it is a diving watch. The warm air in the room will cause the seals in the watch to expand, the temperature shock of when you step outside into the colder air of the rest of the building will cause the seals will contract and allow a tiny amount of moisture inside the case. Over a period of time between services this can cause the hands and dial of a watch to rust, even if the watch is rated at 300m or more.