The replacement of a battery in a dive computer and associated testing. 
Whenever we carry out repair work or a battery change to a dive computer we perform a pressure test which will indicate whether all the dive computer seals are fully intact and properly seated. We always follow a set routine when pressure testing that will make it obvious to the technician that there is a problem without causing any water damage to the internals of the computer.
To carry out the test we need a chamber that provides both air and water pressurisation like the one shown here. As with all things, a good, reliable and accurate test chamber is expensive. To begin we suspend the computer in the air and then pressurise the chamber to approximately four atmospheres. Should the dive computer have a damaged seal around any of the push buttons or battery compartment this will allow harmless air to be forced into the spaces.