Water resistant watches – the case, crown, push buttons and crystal of a watertight watch are made in such a way that no dust or water can penetrate, providing longtime protection of the internal parts.  Water-resistant watches should be tested once a year and opened only by a qualified watchmaker.  Most manufacturers avoid the term “waterproof” as no international standard has been devised.  Waterproof is not a legal term in the US.  Water resistant watches can have the following features:

• Screw-lock crown – a crown that can be screwed into the case to make the watch watertight.
• Tidal watches – indicate high and low tides.  A must for yachtsmen.
• Yacht timer – a countdown timer (see “count-down timer”) that sounds warning signals during the countdown to a boat race.
• Diver’s watches – watches able to withstand water pressure up to a specific depth without incurring damage.  These can have the following features:
• Depth sensor/meter – a device on a diver watch that determines the wearer’s depth.
• Depth alarm – an alarm on a diver’s watch that sounds when the wearer exceeds a pre-set depth.  In most watches in stops sounding when the diver ascends above that depth.
• ATM – 1 atm is the pressure of 1KG/cm2 and corresponds to 10 meters of depth.
• Altimeter – a device that determines altitude by responding to changes in barometric pressure.