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rick,

i still stick with "hogwash".

physical chemistry class will prove all of this.  are there any 
physical chemists or chemical engineers out there besides me?  
where is lori boock when i need her?  the gas doesn't stratify in 
your tanks.  you don't need some convoluted bent valve stem to 
give some sort of vortex/swirling of the gas.  this is all 
"blatant strokery" to quote our good friend.

people are seeing different values for their mix after they wait 
a day, but nobody has done a real cause/effect analysis on why 
this is happening.  what if you laid it on its side for 6 hours 
and farted on the cylinder three times in rapid succession.  then 
you analyze, and the number is different.  now everyone assumes 
it was the farting and starts doing it.  please read chapter 9 of 
robert pirsig's "zen and the art of motorcycle maintenance" to 
get a real understanding of what i am talking about here.  better 
yet, read the whole book.  (sorry about the farting for whoever 
was offended - i couldn't resist)

any residual gas in the valve stem should not be a problem.  i 
alway purge that first to blow any funk out of my valve before i 
hook up my flow regulator.  you are using a flow regulator with 
your analyzer, aren't you?  if not, there is a source of error.  
and again, the analyzer is ONLY good to +/- 2% if you have a 
miniox like me.  read the owners manual.

i don't know who represents the cga.  they are probably not 
chemical engineers and chemists.  maybe some mechanical 
engineers plus a lot of technician and administrative government 
type people that like to decide what you can and cannot do, but i 
just don't know.  wait until they come up with a new connection 
for eanx (i heard it is a reverse din) that forces us to buy a 
lot of new stuff or start home brewing.  i home brew.  i don't 
want anybody else messing with my tanks for my dives.  the person 
diving the gas is a lot more interested in making sure it is 
right.  why they suggest the rolling is probably tied to my 
farting analogy.  btw, how do i roll my doubles <g>?  if you want 
to roll your tanks, have at it.  the molecules will take care of 
themselves.  

the biggest problem is temperature.  the gas has to have reached 
ambient temperature or it will be cooling as you are analyzing.  
also, the gas will be cooler as it exits the tank due to 
expansion (like your a/c freon).  the analyzer cannot correct for 
temperature.  your calibration gas, unknown gas, and analyzer 
really need to all be at ambient temperature and at equilibrium.

and that is my 5 minute chatauqua for now.

scott

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