How much impermeable is your watch?
Watches are usually considered and defined by the same Watchmaker companies as water resistant. It is important to know that in watchmaking protecting the case from external substances is an essential requirement to ensure the correct functioning of the device. This is the origin of the important indication of impermeability, which qualifies a case whose clefts are protected (with different systems such as gaskets, screw closings, etc.) against water, but primarily against dust and filth.
A watch is stated to be “étanche” or water resistant when it passes a test which does not include water: the watch is closed in a special container and exposed – for samplings – to a pressure of 2 or 3 bar (that means 20 and 30 meters respectively without disturbances, such as dives, streams or movements which change the normal pressure exerted by water). What conclusion should one draw? That those watches which have borne the pressure of 2 or 3 bar, or supplied with the notice “until 30 metres” (and those of the best Brands almost all are) do not have to be immersed in water, although they can provide a high resistance against the liquid which should, by chance, come into contact with their case. This indication must be interpreted as a guarantee of good case closure.
Instead, if a watch in stated to be “plongeur”, waterproof or diver, it must have proved – one by one! – to bear a pressure of at least 10 atmospheres (corresponding to 100 metres under sea level) and pass a test of impermeability in water with a minimum pressure of 12.5 bar (higher than the guaranteed bore pressure). These are watches supplied with adequate glass, case back, crown or buttons closure, in case of chronographers, to bear water immersion, such as special types of gasket or screw closures.
Remind that the real impermeability is just the one guaranteed by the notice “100 metres” or “10 atmospheres”!