A Brief Introduce of Watch（From Wikipedia, the free encyclopedia）

A watch is a timepiece, typically worn either around the wrist or attached on a chain and carried in a pocket. Wristwatches are the most common type of watch used today. Watches evolved in the 17th century from spring powered clocks, which appeared in the 15th century. The first watches were strictly mechanical. As technology progressed, the mechanisms used to measure time have, in some cases, been replaced by use of quartz vibrations or electronic pulses. The first digital electronic watch was developed in 1970.

Before wristwatches became popular in the 1920s, most watches were pocket watches, which often had covers and were carried in a pocket and attached to a watch chain or watch fob. In the early 1900s, the wristwatch, originally called a Wristlet, was reserved for women and considered more of a passing fad than a serious timepiece. Men, who carried pocket watches, were quoted as saying they would "sooner wear a skirt as wear a wristwatch".This changed in World War I, when soldiers on the battlefield found pocket watches to be impractical and attached their watches to their wrist by a cupped leather strap. It is also believed that Girard-Perregaux equipped the German Imperial Navy with wristwatches in a similar fashion as early as the 1880s, to be used while synchronizing naval attacks and firing artillery.

Most inexpensive and medium-priced watches used mainly for timekeeping are electronic watches with quartz movements.Expensive collectible watches, valued more for their workmanship and aesthetic appeal than for simple timekeeping, often have purely mechanical movements and are powered by springs, even though mechanical movements are less accurate than more affordable quartz movements. In addition to the time, modern watches often display the day, date, month and year, and electronic watches may have many other functions. Watches that provide additional time-related features such as timers, chronographs and alarm functions are not uncommon. Some modern designs even go as far as using GPS technology or heart-rate monitoringcapabilities.

Water Resistant Mark

Water Resistant is a common mark stamped on the back of wrist watches to indicate how well a watch is sealed against ingress of water. It is usually accompanied by an indication of the static test pressure that a sample of newly manufactured watches was exposed to in a leakage test. The test pressure can be indicated either directly in bars, or as an equivalent water depth in meters.

An indication of the test pressure in terms of water depth does not mean that the watch was designed for use in such water depths. For example, a watch marked at 30 meters depth cannot be expected to withstand activity in a swimming pool, let alone continue to function at 30 meters under water. This is because the test is conducted only once using static pressure on newly manufactured watches. In practical use, a watch is subjected to variations in pressure which can add pressure to the static pressure of the water. Examples of this include the movement of a swimmer's arm through the water, or violent sprays encountered in water skiing. The test for qualifying a diving watch for repeated usage in a given depth includes safety margins to take factors in account like aging of the seals, rapidly changing water pressure and temperature, as well as dynamic mechanical stresses encountered by a watch.

ISO 2281 water-resistant watches standard

The International Organization for Standardization issued a standard for water resistant watches which also prohibits the term waterproof to be used with watches, which many countries have adopted. The international standard ISO 2281 Horology -- Water-resistant watches defines the water resistance of watches. This standard was only designed for watches intended for ordinary daily use during exercises under water for a short period under conditions where water pressure and temperature vary.

The ISO 2281 standard specifies a detailed testing procedure for each mark that defines not only pressures but also test duration, water temperature, and other parameters. Besides this ISO 2859-2 Sampling plans indexed by limiting quality (LQ) for isolated lot inspection and ISO 2859-3 Sampling procedures for inspection by attributes -- Part 3: Skip-lot sampling procedures concerning procedures regarding lot sampling testing come into play, since not every single watch has to be tested for ISO 2281 approval.

ISO 2281 water resistance testing of a watch consists of:

Immersion of the watch in 10 cm of water for 1 hour.

Immersion of the watch in 10 cm of water with a force of 5 N perpendicular to the crown and pusher buttons (if any) for 10 minutes.

Immersion of the watch in 10 cm of water at the following temperatures for 5 minutes each, 40°C, 20°C and 40°C again, with the transition between temperatures not to exceed 5 minutes. No evidence of water intrusion or condensation is allowed.

Immersion of the watch in a suitable pressure vessel and subjecting it to the rated pressure for 1 hour. No evidence of water intrusion or condensation is allowed.

Exposing the watch to an overpressure of 2 bar, no more than 50µg/min of air is allowed to get inside the case.

No magnetic or shock resistance properties are required.

No negative pressure test is required.

No strap attachment test is required.

No corrosion test is required.

In practice, the survivability of the watch will depend not only on the water depth, but also on the age of the sealing material, past damage, temperature, and additional mechanical stresses.

None of the tests defined by ISO 2281 are suitable to qualify a watch for scuba diving. Such watches are designed for everyday life and must be water resistant during exercises such as swimming. They can be worn in different temperature and pressure conditions but are under no circumstances designed for diving with underwater breathing apparatus.

ISO 6425 divers' watches standard

The standards and features for diving watches are regulated by the ISO 6425 - Divers' watches international standard. Diving watches are tested in static or still water under 125% of the rated (water)pressure, thus a watch with a 200 meter rating will be water resistant if it is stationary and under 250 meters of static water. The testing of the water resistance is fundamentally different from non-dive watches, because every watch has to be fully tested.

ISO 6425 water resistance testing of a diver's watch consists of:

Immersion of the watch in 30 cm of water for 50 hours.

Immersion of the watch in water under 125% of the rated pressure with a force of 5 N perpendicular to the crown and pusher buttons (if any) for 10 minutes.

Immersion of the watch in 30 cm of water at the following temperatures for 5 minutes each, 40°C, 5°C and 40°C again, with the transition between temperatures not to exceed 1 minute. No evidence of water intrusion or condensation is allowed.

Immersion of the watch in a suitable pressure vessel and subjecting it to 125% of the rated pressure for 2 hours. The pressure must be applied within 1 minute. Subsequently the overpressure shall be reduced to 0.3 bar within 1 minute and maintained at this pressure for 1 hour. No evidence of water intrusion or condensation is allowed.

For mixed gas diving the watch has to be immersed in a suitable pressure vessel and subjecting it to 125% of the rated pressure for 15 days in a (helium enriched) breathing gas mix. Subsequently the overpressure shall be reduced to normal pressure within 3 minutes. No evidence of water intrusion, condensation or problems caused by internal overpressure are allowed.

An optional test originating from the ISO 2281 tests (but not required for obtaining ISO 6425 approval) is exposing the watch to an overpressure of 2 bar, no more than 50µg/min of air is allowed to get inside the case.

Except the thermal shock resistance test all further ISO 6425 testing should be conducted at 18 to 25°C temperature. The required 125% test pressure provides a safety margin against dynamic pressure increase events, water density variations (seawater is 2 to 5% denser than freshwater) and degradation of the seals.

Movement induced dynamic pressure increase is sometimes the subject of urban myths and marketing arguments for diver's watches with high water resistance ratings. When a diver makes a fast swimming movement of 10 m/s (32.8 ft/s) (the best competitive swimmers can not nearly swim that fast) physics dictates that the diver generates a dynamic pressure of 0.5 bar or the equivalent of 5 meters of additional water depth.

Besides water resistance standards to a minimum of 100 meter (330 ft) depth rating ISO 6425 also provides minimum requirements for mechanical diver's watches (quartz and digital watches have slightly differing readability requirements) such as:

The presence of a unidirectional bezel with at least at every 5 minutes elapsed minute markings and a pre-select marker to mark a specific minute marking.

The presence of clearly distinguishable minute markings on the watch face.

Adequate readability/visibility at 25 cm (9.84 in) in total darkness.

The presence of an indication that the watch is running in total darkness. This is usually indicated by a running second hand with a luminous tip or tail.

Magnetic resistance. This is tested by 3 expositions to a direct current magnetic field of 4,800 A/m. The watch must keep its accuracy to +/- 30 seconds/day as measured before the test despite the magnetic field.

Shock resistance. This is tested by two shocks (one on the 9 o'clock side, and one to the crystal and perpendicular to the face). The shock is usually delivered by a hard plastic hammer mounted as a pendulum, so as to deliver a measured amount of energy, specifically, a 3 kg hammer with an impact velocity of 4.43 m/sec. The change in rate allowed is +/- 60 seconds/day.

Chemical resistance. This is tested by immersion in a 30 g/l NaCl solution for 24 hours to test its rust or corrosion resistance. This test water solution has a salinity comparable to normal seawater.

Strap/band solidity. This is tested by applying a force of 200 N to each springbar (or attaching point) in opposite directions with no damage to the watch of attachment point.

The presence of an End Of Life (EOL) indicator on battery powered watches.

Watches conforming to ISO 6425 are marked with the word DIVER'S to distinguish diving watches from look a like watches that are not suitable for actual scuba diving.

Most manufacturers recommend divers to have their diving watch pressure tested by an authorized service and repair facility annually or every two to three years and have the seals replaced.

Water resistance classification

Watches are classified by its degree of water resistance, which roughly translates to the following (1 meter = 3.2808398950131 feet):