Glossary
Water resistance and ATM ratings
water resistance ATM
Water resistance ratings (ATM, bar, or meters) describe resistance to pressure in a lab test. They aren't a blank check for swimming, showering, or diving unless the rating, crown design, and gasket condition all support it.
How to read the numbers
One ATM equals about 10 meters of static pressure in a lab, which isn't the same as swimming to that depth. As a rough guide: 30m (3 ATM) means splashes only for most watches. 50–100m means light swimming for many modern watches if the crown is secure. 200m and up is real dive territory when the watch is built for it. Screw-down crowns help, but not if the gaskets are old.
Real-world caution
Hot showers, soap, and age wear out seals. Ratings on vintage watches describe how they left the factory, not how they are today. If you need a watch for water, look for a recent pressure test and an honest rating, not a big number on the dial.
FAQ
What does 10 ATM mean?
About 100 meters of lab pressure resistance. Many 10 ATM watches handle swimming when the seals are healthy. Still, don't operate the crown underwater, and have it retested after service or a hard knock.
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