Is my Mondaine waterproof?

No!  But it is water resistant.

Water Resistant is a common mark stamped on the back of wrist watches to indicate how well a watch is sealed against the ingress of water. It is usually accompanied by an indication of the static test pressure that a sample of newly manufactured watches were exposed to in a leakage test. The test pressure can be indicated either directly in units of pressure such as bar or (more commonly) as an equivalent water depth in metres (in the United States sometimes also in feet).

The two most common markings found on the back of Mondaine watches are:

30 100 3 which means it has been tested at 30m, 100ft, 3 atm, and

100 300 10 which equates to 100m, 300ft and 10 atm.

An indication of the test pressure in terms of water depth does not mean a water resistant watch was designed for repeated long-term use in such water depths. For example, a watch marked 30 metres water resistant cannot be expected to withstand activity for longer time periods in a swimming pool, let alone continue to function at 30 metres under water. This is because the test is conducted only once using static pressure on a sample of newly manufactured watches. The test for qualifying a diving watch for repeated usage in a given depth includes safety margins to take factors into account like aging of the seals, the properties of water and seawater, rapidly changing water pressure and temperature, as well as dynamic mechanical stresses encountered by a watch.  This adds to the importance of changing seals at battery replacement time for example.

So what in practical terms does this mean?

3 ATM activities at this depth might include accidental splashing from hand washing or rain, but not washing up.

5 ATM – will cope with the above plus showering or swimming in shallow water

10 ATM – will also cope with swimming or snorkelling

30 ATM – will also cope with skin diving

50 ATM – will also cope with Scuba Diving

The first indication that you have water ingress is a slight misting on the inside of the glass.  IMMEDIATE action is required by a qualified watch repairer to dry the watch out before rusting occurs.  See the post on How To Get My Mondaine Repaired

The weakpoint of all watches is the crown adjuster which alters the date or time.