Buhlmann deco question

[emmbee]

Hi all,

I'm new here, sorry if this is the wrong forum or a stupid question.

I picked up Deco for Divers (Mark Powell) last WE (which I loved), and was looking at the Buhlmann ZH-L16A tables.

Now, my understanding is that Buhlmann came up with the a/b values first (themselves derived from the compartment half-times), then converted that to the Workman-style M0/delta M so-called "A set", which was found to be overly agressive, and tightened as the B then C sets. This only affected the M0 values. The a/b values are correct to the 4th decimal as computed from the half times, and the closest M0 match (modulo some dodgy rounding) is the A set, so that makes sense. Is that correct?

I couldn't help but notice, however, that the delta M (which is the same for all 3 sets) was wrong for compartment 4. Try I as might, 1/.7725 is 1.294498381877023, not 1.2780. All other delta M match.

What's funny is that every set of tables I could find on the web have those same value from b and/or delta M. So either everybody just cut and pasted the values without checking, or I'm missing something :shocked2:

Any idea?

Cheers,

emmbee

 

[Atomic_Diver]

English please..lol.. I dont know to much detail about it, but i am sure someone on here does..

 

[Mr Carcharodon]

I do not have Powell's book in front of me, but are you comparng equivalent time constants? Workman used 5, 10, 20, 40...minutes; while Buhlman used 4, 5, 8, 12.5...minutes for ZH16A. If you compare the 40 minute Workman to the 38.3 minute Bulhmann you have m-naughts of 56 and 58.5 fsw respectively. Which are at least similar. Given the precision that DCS sysmtoms can be deterimined they seem to be close enough.

By the way Erik Baker's paper "Understanding M-values" has a good compilation of m-values from different sources.

 

[Diver0001]

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A ScubaBoard Staff Message...

I moved this question to the Dr. Deco forum. There's a better chance of Dr. Powell seeing it here

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R..

 

[emmbee]

Hi again,

Got some info from the AP valves inspiration rebreather list: forum.technicaldiving.ie/index.php/topic,1836.msg11375/ (not allowed to post URLs, sorry).

Apparently, there is a minor mistake in the Buhlmann tables, but nobody's too sure where it comes from...

Cheers,

emmbee

 

[adm3745]

If you go on thedecostop.com and post, you may get some good information.