Don't know that specific machine, but the explanation is most likely:
As you get shallower, it becomes harder to reach the 1.4 you've set - in fact, above 12 fsw it is impossible, even if the counterlung is 100% oxygen - so what you've told it to do is pump more oxygen than physics allows, and the stupid machine is only trying to do what it has been told to do.
Rick
As you get shallower, it becomes harder to reach the 1.4 you've set - in fact, above 12 fsw it is impossible, even if the counterlung is 100% oxygen - so what you've told it to do is pump more oxygen than physics allows, and the stupid machine is only trying to do what it has been told to do.
Rick