Do you know the gas your actually breathing some other way.That's his gas selection, it tell the computer what gas he has in the tank, the 3 numbers in the middle are the computer telling him the partial pressure of o2 he is currently breathing.
With that and the depth reading we can calculate the aproximate composition of the gas he is breathing.
In that screenshot it's close to 16% oxygen and the only gas left is nitrogen. Making his mix more narcotic and denser than air.