Watch water resistance: what 5, 10 and 20 ATM really mean. The video guide

Chapters

1. 0:00Five ATM, fifty metres: a depth?
2. 0:21What the number measures
3. 0:49What real life puts it through
4. 1:25The real ATM scale
5. 1:48The word Diver's (ISO 6425)
6. 2:11Where to read the rating
7. 2:19The right habits
8. 2:35The warranty, and what to remember

Transcript

On the back of your watch, a number: five ATM. Sometimes, fifty metres. Many people read it as a diving depth. It isn't one. It's a test pressure. And that mix-up drowns more watches than you'd think. That number comes from a laboratory test. A brand-new watch, perfectly still, in a tank. The pressure rises slowly, holds for a few minutes, then comes back down. One ATM is about one bar. Fifty metres is the pressure of a fifty-metre column of water, on a new watch that doesn't move. A pressure, not a depth. On your wrist, nothing stays still. First, the crown: pulled out, or unscrewed by a quarter turn, and water resistance drops to zero. Then the seals: chlorine, salt, sun cream, soap. They harden, and they crack. A brand-new ten ATM watch can fall below five ATM within three to five years, without a service. And thermal shock: a hot bath, then cold water. The seals expand, then contract. The real scale. Three ATM: rain, hand washing. Five ATM: the occasional shower. Not the pool. Ten ATM: the pool, the sea, snorkelling. Twenty ATM, with the word Diver's: recreational diving. Sauna and steam room: never. Diver's means the ISO sixty-four twenty-five standard. The watch is tested at a hundred and twenty-five percent of its rating. Then for shocks, magnetism and thermal shock. Readable in the dark, with a bezel that only turns one way. Without that word, it's not a dive watch, whatever the number. To read the rating, turn the watch over: the case back is what counts. On the dial, it's only a reminder. Before the water: crown pushed fully in, or screwed down. After the sea or the pool: a rinse in fresh water. And a water resistance test at the watchmaker every two years, and after every battery change. Good to know: the manufacturer's warranty does not cover water resistance. Stick to what your rating allows, and always close the crown properly. To swim, go for ten ATM. To dive, the word Diver's. Discover a whole selection of water-resistant watches at Montres Outlet.