Watch School

Analog Watch

In time context means analogue display that the clock displays the time using the opposite hand analog display, digital display where the time is displayed on an LCD display.


A watch with alarm has some sort of reminder.

Anti-glare Treated

The glass of a watch is often anti-glare, in praktieken this means that you can check the time even though the sun is shining on it.


ATM stands for the atmospheric pressure, when a watch is immersed in water so arises a pressure. An ATM is approximately 10 meters.

To be able to swim with a watch it is recommended to withstand 10 ATM which is about as much as 100 meters.

If you want to dive with his watch it is recommended to withstand 20 ATM.

Arabic numerals

Arab merchants introduced in medieval times the numbers we use today in the Western world.

They are therefore called Arabic (0, 1, 2, 3, 4, 5, 6, 7, 8, 9).


See quartz.

Battery Indicator

A watch with battery indicator shows have an indicator that shows when the battery is running low and need to be replaced.


The case is the shell which the watch is mounted in.

It can be made of materials such as steel, gold, titanium or platinum.


The diameter of a watch refers to the measurement of the outside of the watch between three o’clock and nine (excluding crown).

Perpetual Calendar

A perpetual calendar takes into account month length and leap years.

A leap day is added every year that is evenly divisible by four, however, there are exceptions when the year is divisible by 100 but not the 400th.

This means that, for example, in 2100, 2200, 2300 and 2500 are not leap years even though they are evenly divisible by four.

Only the most sophisticated watches with perpetual calendar takes into account these exceptions.

Happy Watch

When a clock is ten minutes past ten or ten minutes in two so it is said that the clock smiles. Watches photographed in a marketing context usually photographed when they are happy.


The glass of a watch comes in two main varieties: sapphire and mineral glass.

Most exclusive watches manufactured nowadays has sapphire crystal.

Sapphire glass is very scratch resistant.

Mineral glass has the advantage that it is not possible to pieces if crushed.


GMT, Greenwich Mean Time, the time zone that is defined to coincide with the UTC (Coordinated Universal Time).

UTC is the basis for civil times and keep using atomic hear much precision.

In time context means GMT to clock supports two time zones.

Power reserve

Power reserve is the time a bell goes after it became assignments (or kinetically charged).

Quartz has a running time that lasts the time between battery replacement.

Power reserve indicator

Some watches have a display that shows how much spare time you have left.

This dislay called power reserve indicator


The height is measured from the bottom to the top of the watch.


To minimize friction and increase time accuracy so used jewels as bearings in time the system is on a watch.

Jewels manufactured in the same manner as sapphire glass (often used for glass in a watch).

When a movement has many jewels as suggesting it is often of good quality.


Caliber refers to the movement of a watch and its movement.

An advanced caliber can run several complications like chronograph, perpetual calendar and minutrepetion.

Indirectly, it is also the caliber that determines how long the power reserve a watch has.


Ceramics is an increasingly common material used in the manufacture of watches.

It is a very durable and scratch resistant material.

The material also has the advantage that it retains its color and luster over time.


A watch that has extra features such as chronograph, perpetual calendar, etc. have complications.

A watch with many such complications (extras) is called “grande complication”.


The crown is a button that is used among other things to set time and date, and turn up the watch.

It is usually placed at three o’clock on the clock.


Chronograph is a complication that is used to measure time intervals.


A chronometer is a watch that went through precision tests at an independent institute.


Quartz is a rock crystal in the watch industry, in that it is set into vibration by an electronic circuit.

Today they use synthetic crystals that after grinding can keep a very constant frequency.

Quartz watches are usually very accurate and is also known as battery-powered watches.

Mechanical, Automatic

In a preferred automatic watch a drive spring up through a rotor, the energy of the rotor to move, the kinetic energy of the carrier provides.

If the wearer puts down the watch to keep the generated energy (once reserve) watch running.

Power reserve typically lasts one to three days.

Mechanical, Manual

A mechanical watch is pulled up by hand.

The energy generated (once the reserve) is usually one to three days.


PVD (Physical Vapour Deposition) is a surface of a material.

This provides a surface that is durable and has low friction.


Mother of pearl (MOP, eng. Mother of Pearl) is also called Nacre and is an organic composite materials.

The material is sometimes used in the manufacture of dials.

Tissot was the first brand to manufacture a watch entirely of nacre.

Bezel ring

The ring or bezel is the metal frame is attached to the watch glass the watch face with.

It can be fixed or variable in one or both directions.

Screw Crown

Screw Crowns are often used in diving bells, the crown is screwed in to water should not be allowed to enter.

Helium valve

A valve for deep sea diving from diving bells can be used to prevent overpressure in the watch.


A tachometer is a scale for measuring velocities.

Tachometer convert seconds (maximum 60) to kilometers per hour.

To use the tachometer so, a reference distance is provided.


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-resistant rating is based upon optimum conditions in a laboratory. Real life experience & aging of the gaskets will effectively decrease the manufacturer’s specifications of water resistance over time. When water comes in contact with the movement, it is the worst scenario that can happen to a watch – 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.

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 a case or 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 but not immersion.
Case-backs attached with screws would be 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 swimming & immersion in a pool.
Screw-in case backs are threaded and screws into the actual case. This creates a double seal, using both the threading & the gasket as a seal. Generally, (although not the rule) 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 Menuswater 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 & screw 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 opened 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.

3. Gaskets:

“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.
Gaskets begin to erode and break down over time, diminishing the water resistance of a watch. It is important to test you watch once a year for water resistance. Any competent watch maker 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 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 into 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 seeped into the watch prior to immersion & the watch is not water resistant. This method is generally used as a second test to pin-point the problem area.


ATM is short for “Atmosphere” which is equal to 10 meters. Another word for ATM which is commonly used in Europe is BAR – this too is equal to 10 meters.

Helium Escape Valve

The Helium Escape/Relief Valve is used only in extreme 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. The helium is added to remove toxic air created by the extreme depth.

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 needs to escape from the watch at the same speed as the decompression – otherwise the pressure in the watch will pop the crystal off. To avoid that, Omega developed the helium escape valve which allows the helium to escape faster than it seeps in. 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.

The helium escape valve never needs to be used in regular scuba diving unless diving in a controlled environment as described above.

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.

Water Resistance Guide
No Rating – 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 poolside swimming
100m/330ft – 200m/660ft Allows for swimming, snorkeling and showering (do not expose to hot water)
200m/660ft – 500m/1650ft Allows for impact water sports such as board diving and scuba diving
500m/1650ft + Appropriate for serious deep water 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.

Our Recommendations

• Have your watch water-tested once a year.
• Do not shower or swim with your watch unless it is rated 100m/330ft & has a screw-down crown.
• 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 in 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.