Pressure Testing Watches. Necessary or Not?
If a watch is water resistant to a certain depth, and the back is opened to replace a battery, a Pressure Test will check the watch is still water resistant!
Some notes on Water Resistance. A watch that is Water Resistant to 30m is not capable of diving to a depth of 30 metres! These water resistance markings are determined by International Standard ISO 2281. For example 50m watch can be used for swimming and a 100m watch can be used for watersports such as snorkelling and surfing. International Standard ISO 6425 applies to Diving watches and a watch needs to be stamped with a minimum of 200m with the word "Divers" to be used for actual Scuba Diving. ( Apologies I digress)
So to ensure a Water Resistant watch is still Water Resistant after battery replacement it requires a Pressure Test. This test will not make the watch water resistant, it may well fail the test. If it does fail, then your watchmaker can advise you as to steps that can be taken to make it water resistant again. ie. it may need a new back seal, crown(winder) or glass replacement.