the JLC mechanism is with a membrane that expands and contracts according to the water pressure exercised on it.
The brilliant idea governing this mechanism was sparked in minds of JLC engineers by the Atmos clock.
As we know the Atmos mechanism is driven by a gas capsule that expands and contracts according to the variations in atmospheric pressures.
This principle has been applied to creating the depth gauge of the JLC watch.
Regards
Yannis