While not technically part of a watch’s anatomy, it is important to have a good understanding of what the phrase water resistance means and how it applies to a wristwatch. The term “waterproof” is not allowed by the Federal Trade Commission in the United States. This is because under the proper conditions, anything can leak. The phrase “waterproof” is used in almost all of the rest of the world. A watch is generally considered water resistant if it can withstand the pressure of 30 meters (99 feet). Sometimes a watch’s water resistance is referred to “atmospheres.” An atmosphere or “ATM” is 10 meters or 33 feet, therefore a watch that is water resistant to 3 ATMs is water resistant to 99 feet.
The Bar is a unit of pressure measurement that is essentially equivalent to an ATM. If a watch displays that it is pressure resistant to 3 Bar, it would be water resistant to 99 feet.
Many professional dive watches are equipped with a helium escape valve, a watch feature geared towards professional deep sea divers. It allows the extreme pressure from the depths of the sea to escape the watch via a valve that automatically opens when the pressure is greater inside the watch than outside.
In many ways, shock resistance is even more important to a watch than water resistance. A wristwatch is subject to a lot of movement, sometimes sudden, and with a great deal of force. If a watch is not properly shock resistant, it is incredibly easy to impact the movement and damage it. There are several methods watchmakers use today to make movements shock resistant. One of the most common is the Incabloc system introduced by Universal Escapements, Ltd. of Switzerland in 1933. The Incabloc system allows the most sensitive parts of the movement to move sideways when impacted by a shock and then return to its normal position under presesure of small springs above the movable carriage. Most other shock resistant assemblies work off a similar principle to the Incabloc, using springs as shock absorbers.