Whether the watch is waterproof or not depends on whether there is an “ATM” on the watch.
In the description of degree of waterproofing, ATM stands for "atmospheric pressure," which is equal to a pressure of 10 meters deep.
The other word for barometric pressure is bar that often used in Europe.
Waterproof performance level:
The table with the lowest waterproof rating is only marked "waterproof". This watch can withstand water splash but it must not be submerged in water.
At the next level, the most common indication is a waterproof depth of 50 meters, indicating that the watch is suitable for swimming;
The next highest level of water is 100 meters deep, indicating that the watch is suitable for swimming with a snorkel;
Followed by a waterproof depth of 200 meters, which is suitable for recreational diving using a diving respirator;
Still further incredible 1000 meters deep.
How to test the waterproofness:
(1) Apply air pressure to the watch and measure whether the watch case is inflated by air leakage. If it is swollen, it means that the watch is not waterproof.
(2) Apply air pressure to the watch first, then immerse the watch in water. If the watch bubbles up when it is underwater, it means the air has penetrated into the watch before it is immersed in water, so the watch is not waterproof.
(3) Place the watch in a chamber full of water and pressurize it with the piston. If water enters the table, it means that the watch is not waterproof. (This is obviously the most dangerous waterproof test method).