Watches

Just check what the user manual says because it will be different depending on each brand and what standards they follow. Generally speaking it's something like this:

- 3 atm or 30 m: Suitable for everyday use. Splash/rain resistant.Not suitable for showering, bathing, swimming, snorkeling, water related work, fishing, and diving.

- 5 atm or 50 m: Suitable for everyday use, showering, bathing, shallow-water swimming, snorkeling, water related work, fishing. Splash/rain resistant. Not suitable for diving.

- 10 atm or 100 m: Suitable for recreational surfing, swimming, snorkeling, sailing and water sports.Not suitable for diving.

- 20 atm or 200 m: Suitable for professional marine activity, serious surface water sports and skin diving.Suitable for skin diving.

- Diver's 100 m: Minimum ISO standard (ISO 6425) for scuba diving at depths not suitable for saturation diving. Diver's 100 m and 150 m watches are generally old(er) watches.

- Diver's 200 m or 300 m: Suitable for scuba diving at depths not suitable for saturation diving.Typical ratings for contemporary diver's watches.

- Diver's 300+ m for mixed-gas divingSuitable for saturation diving (helium enriched environment).Watches designed for mixed-gas diving will have the DIVER'S WATCH xxx M FOR MIXED-GAS DIVING additional marking to point this out.

So 100m WR can be very different if it follows ISO 6425 or not