Watch water resistant grade introduction

Nowadays we take for granted that most watches are water resistant and by that we assume that we could deep dive with them. In fact, only some of the so called water resistant watches can be used for diving depending on their level of resistance to water pressure.
In a water resistant watch this limit is generally clearly indicated either in the dial or in the back of the case and it is expressed either in meters, feet or atmospheres. If the watch does not indicate the limit but just that it is “water resistant” then the only thing one can do with it is washing his/her hands. Conversely, the limit indicated gives a clear direction about what is possible to do or not to do with the watch.
Unfortunately, the indication of the limit is not clear and for some people it might even be misleading. The following section underlines the meaning of water resistance and what to look at in order to ensure we make the best use of our watches.

Water is the biggest enemy of a watch.
Watch movements are made of many small mechanical parts and sometimes they also include electrical parts (e.g. quartz watches). As such, watch movements should never be in contact with water or other liquids as they might create rust, short cut the electrical system and/or deteriorate the movement over time.
The watch case tends to protect the movement from external factors. For this reason the first water resistant watches, were made via using a secondary water resistant case to house and protect the traditional watch (same technique as the one still used today for some photo cameras). Only in a second stage the watchmakers started developing real water resistant watches. Those were made of materials resistant to water (e.g. stainless steel) and sealed hermetically via leveraging new elements like the o-rings/gaskets generally made of rubber, silicon or teflon.

Watch water resistant grade introduction
Different levels of water resistance.
As mentioned, the simple descriptor “water resistant” is not a guarantee. This mark only indicates that you might keep the watch while washing your hands. In order to use the watch in other occasions that foresee the contact with water it is paramount to understand the level of resistance to water pressure. This last is generally measured in “meters”, “feet” and/or “atmospheres” (indicated as “atm”). It is very important to underline that the measures in “meters” and “feet” do NOT denote the water depth to which a watch can be worn. Those, in fact, refer to the height of a column of water that would generate a specific water static pressure on the watch – for example 1 atm is equal to about 10 meters. However, when worn, the watch is subject not only to static but also to dynamic water pressure.
The resistance to water pressure is measured accordingly to some international standards (e.g. ISO 2281, ISO 6425) and watches are generally grouped in five / six classes depending on their degree of water resistance: water resistant / 3 atm, 5 atm, 10 atm, 20 atm, diver’s watches and diver’s watches for mixed-gas diving. Depending on the class, the watch might be used for different water activities as described in the following table.

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