Huw Porter wrote:

> If I read you correctly, you used your tables to set the profile
> for a 25 minute dive at 35 meters, about 115 feet, on nitrox 32, which
yielded
> a deco schedule totalling 10 minutes with the first stop at 24 meters.

> The 24m stop is a microbubble stop, halfway between max depth and first
> formal stop.  There is no second microbubble stop, cos it would be 24m
> minus 1 ATM, or 14m which is above the first formal stop.

What tables are you using that include a microbubble stop?  If this is
something you're adding yourself, then I suspect you are adding a
microbubble stop to a program that already contains several of them.

You're not the first person I know of that includes a deep stop at half the
difference between max depth and first stop, but this case would seem to
suggest somethng different is appropriate.  I'm sure you didn't fail to
notice that my computer simulator added a minute of decompression just
before I hit the 50 foot mark.  This is a pretty clear indication to me that
it's algorithm is still loading at least one critical compartment.  One of
the things I specifically include in my personal choice of ascent profiles
is a check to see that my computer is not, in fact, showing declining
nitrogen loading, as represented by increasing NDL or decreasing deco time,
at the first optional stop I do.  This is precisely how I decided I'd add my
first optional stop at half my maximum depth rather than half the difference
between that and my first stop.  Of course by the standard of doing the
first stop at half the distance to the first stop, I'd be doing mine at
about the same place since the first mandatory stop is at 10 feet.  I don't
have my hard copy SSI deco tables handy, but I suspect that they would
require something similar to what I computed rather than what you did.

> Yep, but you either have to run with the 'deep stop' idea or not.  However
> the computer/tables model loading or unloading compartments, within my
> (limited) experience, and within my (admittedly 'weenie' profiles) I know
I
> feel good after adding in deep stops.

That's true, but there's nothing that says that I have to run with the same
deep stop idea you are following and you have to admit that a profile that
considers whether there is a critical compartment still loading at the
computed micorbubble stop makes more use of the organic computer and, in my
opinion, better use of the submersible electronic one than a profile that
ignores this element based on something a dry computer recommends.  The
primary difference in this aspect of our respective preferences comes from
the difference in where our systems show that first mandatory stop to be.
If you are adding that deep microbubble stop to a computer program's
recommended stops, I think you're probably adding something that's already
been done correctly by your program.  Then again, I might be wrong.

From my perspective, all of your stops are, in fact, deep stops since all of
them are done below my computed first mandatory stop at 10 feet.

> PPO2 of Nitrox 32 at 33m is pretty much 1.4.  And since Suuntos calculate
> the PPO2 (and MOD etc) as if the mix was actually 32.9, it was running at
> over 1.4.

The essence of this thread, at least at this point, was the relative
conservatism of the Suunto versus tables (meaning the kind of hard copy
tables we all have used rather than a different algorithm on a different
computer that prints results it calls tables) and versus other computers.  I
think we have confirmed the difference since, by your own numbers, your
computer requires more deco than mine.  I think that you'll find that trying
the profiles I suggested will increase the difference, making it even more
obvious, but somebody that actually has one of the computers will have to
confirm or disprove my hypothesis . . . or I'll have to find the Suunto
simulator I stored somewhere and check it myself, which I may do later
today.

Just a suggestion for you, but if you're using one of several computer
generated table sets and adding a deep stop to the results, it might be a
good idea to confirm that the computer has not already incorporated the deep
stop concept into its recommended profile.  If it has, you may actually be
doing a less desirable profile instead of a better one . . . or not.  The
trick is to know for sure, i.e. apply that organic computer some more.

Lee