Why ZH-L8+ and not VPM or RGBM?

memorex77 · Jan 1, 2011

Actually I can't find details about the ZH-L8+ model. Many other dive computers use ZHL16C GF models, or VPM or RGBM, so ZH-L8+ seems like a step back using only 8 compartments.

What exactly is ZH-L8+?
How has it been verified?
How does it consider micro bubbles?
Where do "your" modifications to the model come from?
Why doesn't any other computer or simulation software use this algorithm?
Does the user arbitrarily throw in some deep stops if he is so inclined? (user can chose 0, 1 or 2 min apparently). I thought the model does consider micro bubbles?
How do I plan my dives??

Mod63 · Jan 1, 2011

Hi,

ZHL-8 is (partially) described in Bühlmanns book, which has been co-authored by Ernst Völlm, the owner of UEMIS. ZHL-8 has been verified by trial dives, like most other modells implemented in dive computers and running profiles through it on land and compare them with know good profiles. ZHL-8 has been used in the past by Uwatec since the Aladin, and the version ZHL-8 ADT MB does consider the formation of microbubbles.

Cheers

iztok · Jan 2, 2011

Does any software planner use ZH-L8?

DiverLaura · Jan 2, 2011

the following is Ernst's reply to OP's question.

The fundamentals of the adaptive decompression model ZH-L8 ADT have been
developed in the early 90's in cooperation with Prof. Dr. A. A. Buhlmann.
The decompression algorithm is able to increase safety for cold water
diving, exertion, repetitive- and jojo-diving and violations during the
ascent and the decompression stops. This adaption in real time is possible
by the introduction of variable blood perfusions in muscle- and skin-tissues
and the integration of an algorythm for the formation and reduction of
microbubbles. The variable perfusion and/or the obstruction of local
perfusion due to the presence of microbubbles affect the nitrogen saturation
and the tolerated ambient pressure.

The principles of the algorithm are published in a book (Buhlmann A. A.,
Voellm E., Nussberger P., Tauchmedizin, Springer-Verlag Berlin, 5. Edition
ISBN 3-540-42979-4). Unfortunately, the book is in German language, there is
no English translation.

A number of dive computers use this algorithm since 1994. Skin temperature
is estimated according to water temperature and time. Workload is measured
by monitoring the respiration. Microbubble formation is mainly based on the
pressure/time profile and physical and physiological data. With the logging
features of these dive computers, the model could be verified. Today,
millions of dives have been made with these dive computers.

The algorithm ZH-L8+ has additional enhancements compared with the ZH-L8
ADT. In addition to a few minor changes, it can calculate deep stops and
adds a new method to change the conservatism of the decompression
calculations.

DiverLaura · Jan 2, 2011

a) ZHL-8 is a newer algorithm than the ZHL-16 but has been in extensive use for years.

b) the ZHL-8+ allows the algorithm to essentially be considering the curve on either side of each of the 8 compartments as influenced by the modifiers. Taking that into account its not just 8 compartments, its like an infinite number if that makes sense. this is not changing the base algorithm, but making it hopefully more 'adaptive' and reflect the actual dive you are doing.

memorex77 · Jan 2, 2011

LauraJ:
The algorithm ZH-L8+ has additional enhancements compared with the ZH-L8
ADT. In addition to a few minor changes, it can calculate deep stops and
adds a new method to change the conservatism of the decompression
calculations.

Hi Laura,

Thanks for working on Sunday and for answering many of my questions! If I would buy your product now, what would I exactly do with the above statement, though? Dive into deco and then figure out what the new method to change the conservatism really DOES to my deco? Repeat the same dive to check out that new method with different settings and hope for my gas supply to last long enough?

Don't get me wrong - I believe you have a great computer! Yet there seems a lot of black magic and the least I'd need is simulation software to evaluate what it'd would do to me on my typical dive profiles.

DiverLaura · Jan 2, 2011

the profiles in general will not look _that_ different from what you are used to. if anything, if you are in cold water, have a heavy work load, or are doing zig zag profile it will be more conservative, but not outrageously so.

I realize you are asking most likely about the amount of time on a decompression dive for gas planning reasons, and for that i would say that it's numbers are in the middle range.

All decompression algorithms, be they on your wrist or PC are black magic to a degree.

Ernst understands the end users desire for a dive planner... As i understand it, that is part of the release that will come with Trimix. I have asked him what PC planner setting will be closest in the interim.

DiverLaura · Jan 2, 2011

just getting back to you all re: ZHL-8 planners: To my knowledge (and Ernst's) there is no PC planner for ZHL-8.

The ZHL-8 is also an adaptive algorithm

therefor it is a bit hard to simulate on the surface what you will experience underwater with regards to workload and yoyo profile. For realistic planning purposes it will need temperature, estimated workload (based on SAC) and any yoyo'ing you plan on doing. In computers that have a planner, what you are getting is the base ZHL-8, without the real-time data that will be utilized for ongoing calculations during the dive.

for general gas management planning, in my experience i have not seen it keeping me in the water noticeable longer than other units or PC planners. you can use it with the tank transmitter and have RGT (remaining gas time) based on ascent time (including decompression stops) but generally we do tech dives with enough redundant gas that a couple minutes different here or there is not going make a difference between carrying an AL40 or AL80 of deco. We already have that planned out based on our overall profile long before we hit the water.

MarineResearch · Jan 5, 2011

Skin temperature is estimated according to water temperature and time.

So, how does the Uemis computer know what kind of underwear I have under my drysuit? Is there a built-in camera that spies on me while I'm changing?

iztok · Jan 5, 2011

MarineResearch:
So, how does the Uemis computer know what kind of underwear I have under my drysuit? Is there a built-in camera that spies on me while I'm changing?

I would assume it is compensated somehow by lower SAC rate.

Why ZH-L8+ and not VPM or RGBM?

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