Help understanding second stage at depths below 100m

[kmacas]

Hi,

I have a question.

If the medium pressure from first stage to second stage is let say 10 ATM.
How do you breathe at 120m when pressure of the surrounding is 13 ATM?

 

[tbone1004]

first stages are depth compensating, that means that the intermediate/interstage/medium pressure is x over ambient. so if you are at say 13atm, the interstage pressure will be 23atm.