Multi-level tables

[voidware]

I've heard that PADI instructors have had their certification revoked for teaching multi-level on their standard tables (not the wheel). Nonetheless, an anonymous source taught me how to do it. It's actually really simple, and it works with almost all tables. There are two methods, one involving residual nitrogen time and another with repetitive group letters. I can write a procedure, for those that would like one, but it is just like you would expect--don't add any surface interval. I am sure you guys won't have trouble.

But to get to my question: Does anyone dive with this regularly? Is it safe? and how do the times compare with those given by the wheel?

brandon

 

[Zept]

There was a thread about the Wheel that covered this in passing.

I've tried working problems both ways and I don't always get the same answer -- the Wheel gives a higher pressure group for some dives. For example, for a recent dive I calculated a P with the tables and a Q with the Wheel. Usually it happens when the dive time is right at the limit for a particular PG. For example, 20min at 20m is a G on the table (just), but I get an H with the Wheel. Could just be that I read the Wheel more conservatively.

Although I think the Wheel is expensive, for what it is, I've just given in and bought one. Two reasons: less mental arithmetic, and it gives depths in 2m increments all the way to 40m. On the PADI metric tables, the increment changes to 5m when you reach 25m -- so if you plan a dive to 25m and accidentally drop to 26m, you have to calculate for 30m. One downside of the Wheel is that it's quite easy to get the lines mixed up. I've read the PG off the 14m line instead of the 16m line, for example. It pays to think about the answer -- if it doesn't feel right, it might not be. Same is true with tables, of course.

Unlike almost everyone else in the world, I actually like the Wheel. Then again, I'm sad... and a bit of detail freak.

Zept

 

[Dr Deco]

Dear readers:

Using standard tables for multilevel diving is referred to as “reading the tables sideways.” It does work under most circumstances. That PADI tables do come in smaller depth increments, and that was one of the reasons that they were made by Dr Rogers (and later tested by me).

The advantage of the Wheel is that it is an actually tested device. On reason for the cost, in part, is that it is necessary that it be made very precisely so that all of the disks line up properly (so it has been explained to me).

Dr Deco:doctor:

 

[otter-cat]

Dr Deco,

I was wondering if the precise manufacture of the Wheel you refer to is something that can wear away over time. In other words, after being used for some time, is it possible for the discs to become out of alignment?

I have never used the wheel, so I am not sure what is really involved. However, I am currently undergoing PADI divemaster training, and I know that at some point in the process I will have to learn to use the Wheel. Since it is so expensive, I was thinking of buying a used one, but I don't want to do that if it might not be accurate any longer.

Please let me know what you think.

Thanks,
otter-cat

 

[Liquid]

Ever since the diving computer have become a commom tool, relatively cheep, I dont see to much future for the wheel. using a computer is simpler, and gives much more usefull data. I know it encourages "lazy" diving, but that's human nature, to simplify things.

 

[Dr Deco]

Dear otter-cat:

Being made of plastic, I do not believe that they will wear out. A used one should be OK.

Dr Deco:doctor:

 

[Zept]

Otter-cat, you can check the alignment of a Wheel. There is a small circle on the back plate and a dot on each of the parts that turn. You should be able to line up the dots over the circle, otherwise there is something wrong.

Old wheels can get scuffed and difficult to read, but that's pretty easy to detect .

Hope that helps,


Zept

 

[BRW]

NAUI's old set of Tables are multilevel tables
and have been dived as so for the past 15 yrs.
The NDLs are one group or so less than the USN Tables, and extensive computer testing (16 million
dives)showed that no M-values were ever exceeded
by multilevel dives ALWAYS shallower than the
previous segment.

See Technical Diving In Depth (Best Publishing)
or earlier pubs.

Bruce Wienke
NAUI Counterterror Dive Team Ldr

 

[Dr Deco]

Dear Readers:

Dr Weinke’s posting reminds me of one reason why divers like deco meters, namely, the ability to dive deeper on a subsequent step than the previous. It is an unfortunate reality of tables that there are restrictions on them if they are to be made into a simple, easily readable form. What all prefer is a single sheet that gives a decompression guide that is easily readable.

To accomplish this, certain restrictions apply in the table format. Examples are (1.) a single controlling elimination halftime, and (2.) for multi level dives, the requirement that you move shallower. If one should desire to forgo simplicity, more complicated tables could remove the restrictions. Remember that, while decompression computers do not have such restrictions, the same (or similar) algorithms are in the dive computers as were originally used to create the tables. The difference is that electronics has allowed the miniaturization of the components. We likewise do not need the worry about temperature stabilization of the computer’s components or intolerable power consumption.

All of that would require a really long extension cord!

Dr Deco
:doctor: