Many brands of watches are marked in the instructions or guarantee manual: waterproof 30 meters, only for washing hands splashed wet; Waterproof 100 m for swimming or snorkeling; Water resistant to 200 meters, water lung diving. Many people wonder why they recommend a watch that is more than 100 meters waterproof when buying a watch that can be used for water activities." I've never dived more than 50 meters in my life, "one diving instructor told me. In fact, such a question not only exists in the general purchase of watch consumers, the previous few years most of the watch salesman and repair master are not very concerned about this problem, until the recent sports watch market attention, began to pay attention to the difference between waterproof signs, but also do not know why.
Every time you increase the depth of the water by ten meters, you increase the pressure equivalent to one atmosphere. According to this principle, the general watchmaking is to test the waterproof performance of the watch with the pressure gauge. Therefore, some tabulation will indicate the pressure resistance value, that is, the unit is labeled bar or atm, to indicate its waterproof value. 1bar is equal to one kilogram of pressure per square centimeter, so the pressure resistance of 10bar is equivalent to the pressure of 100 meters below the water surface, and the pressure resistance of 20bar is equivalent to 200 meters of waterproof. The pressure resistance of 3bar is equivalent to 30 meters of water resistance, which is commonly known as life waterproof. The most common situation of the general watch is only marked "Water Resistance" without marking the waterproof value, in fact, in accordance with international standards, it is regarded as waterproof 20 meters.
But why is marking depth so different from actually using it? First of all, the general so-called pressure test is only a static measurement, a few seconds to reach the marked pressure number can be pressurized, but the actual wearing on the user, the case under the environment is dynamic. The hand is the most frequently moved part of the average person, regardless of daily life or water activities, the body often has a large number of movements, if engaged in scuba diving, even if only within 30 meters of leisure diving, in a short time to rise and dive like frequent changes in pressure and pressure.
Moreover, a long time of sun and rain, and dirt and dust will make the waterproof rubber ring in the case and even the case itself age with time, and the general public does not have the habit of regular maintenance or cleaning of the watch. What's more, the test of the general waterproof meter is a sampling inspection system, and each batch of production only needs to extract a few pieces of inspection. This also has a lot to do with the reliability of the brand, I once visited a manufacturer of waterproof diving watches labeled 200 meters, and admitted that the pressure gauge it uses can only test to 10 atmospheres. Therefore, based on the above considerations, the waterproof ability of the case should be considered in accordance with the simple test and then deducted many times the safety factor, for many years, most watchmaking has taken this for granted, and has been used so far.
Diving watch in fact, as early as 1982, The International Standards Organization ISO(The internation for Organization for Standardization) found that the general waterproof table float detection specifications are not enough to provide must face the risk, And take time as an important safety factor to consider the needs of divers, so complete the diving table (Diver' s Watch) standard specifications. And in 1984, a partial revision was made, making the diving watch in addition to the waterproof pressure is different from the waterproof watch, but also additional many strict regulations. First of all, the diving watch requires a waterproof design so that it can actually be placed in the water at least 100 meters, and must meet the following requirements, can be called a diving watch.
Time pre-selection device: must be resistant to accidental rotation and can be used correctly during the dive and at maximum depth. The device must be clearly marked every five minutes. Generally, the most common is the timing outer ring, in order to resist unexpected rotation, most of them are designed so that they can only rotate counterclockwise.
Visibility: At a distance of 25 cm in the dark, you can still see the time setting of the time indicator and the time pre-select device, and you can confirm that the watch is still running.
Magnetic resistance: With resistance to more than 4800 amperes per meter (60 Gauss DC).
Shock resistance: It can withstand the impact of falling at a height of 1 meter.
Salt water resistance: 24 hours placed in 23℃, concentration per liter of 30 grams of salt water, the case does not change, and normal operation.
Reliability under water pressure: Placed in a water container, and pressurized within 1 minute to 1.25 times the pressure of the waterproof pressure marked on the case, and can withstand up to 2 hours.
Water performance: under the water depth of 30 cm, the action is not affected (such as timing outer ring, light button, etc.).
Impact resistance: a, the watch ear (strap and head joint) can withstand 200 Newton tension. b. After 10 minutes of pressurization at 1.25 times the pressure of waterproof pressure in water, the crown can withstand the force of 5 Newton on the vertical surface.
Temperature change resistance: 30 cm in water can withstand sharp temperature changes from 40℃ to 5℃ and then to 40℃ for 10 minutes. The interval cannot exceed 1 minute.
Pressure resistance, water pressure: first pressure to 2 bar test. It is then tested by water pressure. It is placed in a water container and pressurized within 1 minute until the pressure of 1.25 times the waterproof pressure marked on the case reaches 2 hours. Then the pressure is relieved at a rate of 0.3 bar per minute for 1 hour. For example, if the case is marked as waterproof 200 meters, it needs to be pressurized to 250 meters.
The depth marked by the diving watch must be an integer of hundreds, and all functions must maintain their function at this depth for more than a certain time, such as waterproof 100 meters must be able to maintain 1 hour a day under 100 meters of water depth, waterproof 200 meters must be maintained 2 hours a day. And so on. Finally, it must be noted whether the general function of the watch in a helium-oxygen environment will cause damage.
The nature test can be classified according to the style, that is, it can meet the requirements of standard tolerances and defective rates. However, the gas resistance and water pressure must be tested for each one. When the diving watches produced have met the ISO diving watch specifications, it should be marked "DIVER' S LM", L is the waterproof depth. That is to say, if the diving watch you buy has been indicated to meet the ISO specification, not only can you actually use the depth indicated, but each one has been tested for pressure.
Although ISO stipulates the waterproof marking of the watch, because the various countries are still not consistent with the marking specifications of the watch, the general consumer can not tell whether it is in line with the specifications, do not visit the waterproof data marked by the watch only as a distinguishing identification, rather than as the true depth of use. Remember "waterproof 30 meters, only for washing hands splashing wet; Waterproof 100 m for swimming or snorkeling; The principle of "water proof 200 meters, water available for scuba diving" should be foolproof. Of course, don't forget that most of the brands of diving watch waterproof guarantee is only 1 year, regular inspection is very important.