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Dan Nafe writes:
> 
> David Story writes:
> > This discussion is fun, but none of this is provable.  I don't think
> > we can reasonably point the finger at dead air space in second stages.
> 
> maybe not "dead-air", but there IS something about the geometery of the 
> USD second stage that causes these symptoms. The USD and Mares second 
> stages demand valves and associated plumbing are identical (the 
> replacement parts are interchangeable!). The Mares regulators breathe 
> like champs and the USD make u feel uh lifftle fuzzie sumtimess. The 
> difference is in the shape of the second stage.

I really don't want to continue this discussion, so feel free to skip
this message.  

My point is that there are so many other factors that focusing on dead
air space in a second stage is probably misguided.  Even the two
regulators you mention have different first stages, which have a
dramatic effect on breathing effort.

But beyond equipment, the human behavior -- skip breathing and other
behaviors which contribute to CO2 buildup -- have a much larger
effect.  

Now, if you were to argue that the USD regulator has high "work of
breathing" and therefore _contributes_ to CO2 retention, I'd agree.
But the second stage dead space surely cannot be proven to be the cause.
And as someone has pointed out, your sample is not a blind test.
Statistical gaffes of the past show that only controlled tests are valid.

Cheers,

David Story                        	        Silicon Graphics, Inc.
story@sg*.co*					Mountain View, California

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