| Re: gas switch on Shearwater
A gas switch on a CCR 2000 would also require a flush. I think that you are confusing two issues.
At the time, both the CCR 2000 and the MK5 supported "constant PN2." On the CCR 2000, that was implemented by having two diluent tanks, typically air and heliox. You could descend to what you determined was an optimal EAD for narcosis, then switch from your air dil to your heliox. For the rest of the way down, no N2 would be added, so your PN2 would stay constant.
I'm not as familiar with the MK5, but I was told that you could do the same thing on it. As I understand it, that is the way they dived it on the Wakulla 2 project.
Obviously excessive mask clearing could change the mix without the computer knowing, but it seemed pretty cool at the time.
Flushes were a different thing. There was a configuration parameter that you set pre-dive to tell the computer whether you were going to flush when you switched back to the air dil on ascent. Back then, flushing to air on the ascent was a common practise.
I agree, it was an amazing machine in its time. It had great WOB and very capable electronics. The downside was that it was complex and heavy. My experience on the CCR 2000 was one of things that led to my current views on simplicity and "clear mental models."
By the way, Dan Wible is still around. He came down to the dive site to say hello when Paul was teaching his rEvo course in Washington a couple of months ago.
Bruce |