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10 ATM water resistance: what it really means

When a watch displays “10 ATM” on its dial or case back, it indicates its level of water resistance. But what does this value actually represent?

What does “ATM” mean?

ATM means atmosphere, a unit of pressure. One atmosphere corresponds to the pressure exerted by the air at sea level. 10 ATM therefore equals 10 times this pressure, or about 100 meters of water depth in theory.

Please note: this is not a real operating depth

This is the most important point to understand. The 10 ATM value is measured in a laboratory, with a stationary watch. In reality, several factors increase the pressure on the watch:

• Movement (swimming, diving) creates dynamic pressures far higher than simple static immersion
• Temperature and water quality can affect the watertight seals
• Natural wear of the seals over time reduces the actual resistance

This is why manufacturers generally recommend a significant safety margin.

What you can do with a 10 ATM watch

• Wash your hands, in the rain✅
• Shower✅
• Swimming in a pool or the sea✅
• Snorkeling (at the surface)✅
• Scuba diving❌

Why not scuba diving?

Scuba diving generally requires certified water resistance of 20 ATM (200 m) or more, with specific standards (such as ISO 6425 for diving watches), including enhanced resistance tests and often a screw-down crown.

In summary

A 10 ATM watch is perfectly suited to active everyday use, including moderate water activities, but it is not designed for professional diving. The number shown is a guarantee of durability, not a maximum depth to reach.