A watch's water-resistance will always be better if:
- The case (and the crystal) are round
- It has a screw-in crown
- The case back is screwed
- The pushpieces are screwed
- It has a thick crystal
Most gaskets are made from a synthetic material which reacts to heat. Any increase in temperature will cause the gaskets to dilate which reduces the watch's water-resistance. Gaskets are placed at strategic points:
When saltwater evaporates it leaves a film of highly corrosive salt on the gaskets. For this reason, always rinse your watch in fresh water after being in the sea. Gaskets will show signs of wear more or less quickly depending on how the watch is used, and should be changed each year if the watch is regularly worn during water-based activities.
Replacing the battery means opening the case. This must be done by a professional as only they can carry out the necessary water-resistance tests afterwards.