Performance feature of a watch

An essential feature by which the practical value of today's wristwatches is determined, is its water resistance.

To test this, the watch is exposed at the manufacturer to the pressure, which is indicated on the dial or the caseback. The test pressure is measured in atmospheres (atm) or in meters (m) of water column. This means that the manufacturer guarantees that the watch in the shipped status withstands the specified static test pressure.

These are two aspects to be considered

1. During use the watch is exposed to various environmental influences such as dust, corrosive media, extreme temperature fluctuations, etc. Over time this leads to reduced water resistance. Therefore at best the watch should be checked once a year by a watchmaker on water resistance and the seals replaced if necessary.

1. During use in the water the watch will be almost never exposed only static loads but dynamic loads, as movements of the own body, jump into the water, water jets etc. Hereby you can easily produce a water pressure equivalent to a depth of 50 m in a basin, only by moving the arm through the water with a relatively high speed.

From these two points above, the following restrictions apply

1. Dust-protected
2. Waterresistant — Water spray, rain, etc.
3. Waterproof to 3 atm/30 m — car washing etc.
4. Waterproof to 5 atm/50 m — showering, swimming, etc.
5. Waterproof to 10 atm/100 m — snorkeling, diving, etc.
6. Waterproof to 20 atm/200 m — Scuba Diving

For dive watches a water resistance as high as possible is an obvious condition - beneath a number of other additional requirements, such as the measurability of the dive time.

Since Rolex patented the waterproof Oyster in 1926 the usual precaution to achieve the highest possible water resistance is a screw-in crown. In chronographs there accordingly must also be screwed pushers, which can lead to a rather complicated operation. Meanwhile, there are also other modern sealing techniques to achieve a comparable density of up to several hundred meters depth without screwing the crown .

• Das große Uhrenlexikon; Author Fritz von Osterhausen; ISBN 3898804305