Watch knowledge
Watch Water Resistance Explained: ATM, Metres and Upgrades
Understand what a water-resistance rating means, how Phantom Yellow Strike and GA-2100 models differ, and what to check before using a watch in water.
A water-resistance number is a pressure rating, not a promise that you can use the watch at that depth. ATM, bar and metre markings describe test pressure. The right guidance also depends on the watch’s construction, seals and intended use.
In this guide
What do 10 ATM and 200 m mean?
ATM means atmosphere, a unit of pressure. In watch descriptions, 10 ATM is commonly associated with a 100 m pressure rating; 20 ATM with 200 m. Those metre numbers should not be read as a safe swimming or diving depth for every watch.
A static pressure test is different from actual use, and a depth-style marking alone is not a diving certification. For water activities, follow the instructions for your specific watch rather than relying only on the largest number in the description.
Phantom Yellow Strike: standard and upgrade
Phantom Yellow Strike has 10 ATM water resistance as standard. The optional waterproofing upgrade adds 5 ATM, bringing the stated rating to 15 ATM. Choose the upgrade for the watch being ordered and check that it appears in your cart.
The waterproofing upgrade is an order option, not a replacement watch. Different models start with different ratings, so do not apply Yellow Strike’s 10-to-15 ATM figures to the entire collection.
What about Phantom Pulse?
Phantom Pulse uses the GA-2100 platform and is listed with 200 m water resistance. Its analog-digital functions do not mean the buttons should be operated underwater. Keep to the model’s operating guidance, including care for the crown or buttons and seals.
The watch’s appearance does not establish its rating. A metal bracelet, a rubber strap or a dark case finish can all appear on watches with different water-resistance specifications.
Before the watch goes near water
- Check the controls: make sure the crown is fully secured where applicable.
- Leave the buttons alone underwater: follow the model’s instructions rather than testing them yourself.
- Consider its condition: impacts, age and previous repairs can affect the seals.
- After opening the case: ask about a seal inspection and pressure test.
- Avoid heat and steam: a pressure rating does not make a hot shower or sauna a recommended use.
Why pressure testing matters
Water resistance relies on the assembled watch, not just a strong case material. Gaskets, the caseback and the crown or buttons all form part of that system. A pressure test checks the watch under defined conditions; it is not a permanent guarantee that every seal will stay unchanged.
If you are buying for a particular water activity, ask us before ordering and name the activity and model. That is more useful than choosing the largest number without checking its meaning.
For setup and care, visit our watch guides. To understand the case and crystal separately, read our materials guide.
Rating references: Casio’s water-resistance explanation and water-use precautions.
Header image: AI-generated editorial illustration, not a customer review photo. Visit the linked product pages for current watch photos and options.
