Trying to understand why someone would want a liberal computer

[dvleemin]

Hi,
I've seen some discussions on liberal vrs conservative computers, and I was thinking about this. Why would you want a liberal computer? Maybe I'm missing something, but doesn't it make a lot more sense to have a conservative computer? Why take the chance?

Now the obvious answer is you want to go deeper, for longer. But wouldn't it make sense to have a conservative computer that goes into deco mode, and then follow its directions rather than a liberal computer that doesn't go into deco mode? For the little bit of extra time that that deco stops take, isn't it worth the added margin of safety?

Can someone explain this?

DArryl

 

[Bob3]

Dive computers are one of the few pieces of gear that can be safety hazards, even when used as intended.
The pushing of NDLs to the ragged edge has caused the number of so called "undeserved hits" to increase sharply. Resort-type diving is one of the major culprits, where folks will get the deep tissues loaded up.

 

[redacted]

and I now opt for the more libral computer. My wife used a Scubapro EDI which was fairly conservative. I was using an IQ-300 - a bit on the libral side. Problem was that the EDI was regulating our dives, often with differences in NDL time on the order of 5 minutes. I've seen groups of divers where the diver using an EDI was in a deco obligation while all others still had NDL time to burn. Wife and I have since gone to Oceanic computers. These are rated somewhat libral which allows us to control the dive rather than the computer. It's not that I plan to push the NDL. In fact, with the graphic display, our normal plan is to head up when we hit yellow and hang at reat stop until green. But it leave us in control of how extra safe we want to be rather than a conservative computer.

 

[jetblast00]

I use a Aeris Savant, which is very liberal and also goes into deco mode.

Why do I want a liberal computer?
Because I have a good understanding of the tables and numbers that are at play behind it. I want to use my brain to determain my own level of conservatism, not trust a machine to do it for me. If I want to be conservative, then I decide how far to stay from the NDL as reported by the computer, not just trust the computer to build safety into the NDL for me.

When you're writing bills or balancing your checkbook, would you rather use a calculator that always just rounds up to the nearest $10, so that you can feel assured that you are paying enough? No, you want to know the exact info, and then make your own judgements based on that.

 

[dvleemin]

Jet,
I think the chequebook is a poor analogy. Addition and substraction are completly constant and consistant; DCS and tissue loading are not - everything to do with this is not fully understood.

You are making the assumtion that a liberal computer is more accurate than a conservative computer, and I don't think that is necessarily correct. The fact that people occasionally get hit with DCS even after staying within proper limits shows that at least some of the time liberal computers are incorrect. In my mind you're sumply saying that you're willing to chance it, rather than making a good argument for using a liberal over a conservative computer.

As well, you say that you want to trust your brain. But unless you're doing a profile where you go straight down, stay at an exact depth, and then asend, how can you possible calculate the differences as your profile goes up and down? If you take the deepest depth, then your own calculations will reach your no deco limit long before even the most conservative computer.

IMO, its much much better to be safe than push it to the edge and be sorry.

Darryl

 

[large_diver]

I use a Vyper, so I'm not in the liberal "boat", but....

I have to assume there are those out there who are in (a) great physical shape and/or (b) who do so much diving that they may have a better feel for how far they can push things....thus the demand for a more liberal computer...

 

[dvleemin]

large_diver,
I understand that certain people are more likely to get DCS - an overwight, older smoker, you drank the night before is going to be much more suseptable to DCS than a young in shape olypmpic swimmer

But considering that everything with DCS is not fully understood, how can someone know how far to push it? Its not like people have a builtin sense that tells you the current nitorgen levels. And just because something worked one time does not mean it will work the next.

Darryl

 

[Uncle Pug]

Originally posted by dvleemin

As well, you say that you want to trust your brain. But unless you're doing a profile where you go straight down, stay at an exact depth, and then asend, how can you possible calculate the differences as your profile goes up and down? If you take the deepest depth, then your own calculations will reach your no deco limit long before even the most conservative computer.

IMO, its much much better to be safe than push it to the edge and be sorry.

Darryl

Jet's analogy is actually very good...

Darryl, as has already been stated, a liberal computer allows you to set your own conservatism... how would you even know how much extra conservatism to add to a computer that already had some added in to begin with.

It is like using a speedometer that has be purposely set to read high and then you see a traffic cop ahead and wonder if you are under or over...

or like the guy who has someone else set his watch several minutes fast because he is afraid to be late... but he doesn't know how much and so can't make accurate adjustments for contingencies.

....

BTW it is really a bad idea to violate NDL and take a computer into deco mode when all of them (especially your conservative ones) tell you not to do that... they cannot be relied upon to get you out safely. That is really not a very conservative move but unfortunately that is the *thinking* of too many computer divers today. I'm not even going to go into all the reasons that is such a bad idea....

If you plan on getting into a deco situation you need more than a computer.... you need an understanding of staged decompression diving and a couple of good bottom timers and a good depth gauge as well as the skill to hit and stick deco stops.

 

[jetblast00]

Darryl,

I understand your replies, and agree with you a bit.
No, not everything is understood about DCS. But if people haven't figured it out yet, then any computer certainly isn't going to give you any more info. So saying, "People don't understand DCS enough, so I'm just going with what a conservative computer tells me." doen't make much sense either... A liberal computer for me, might be a conservative one for someone else in better shape. And some elderly overweight smokers' Vyper might be way conservative for me, but liberal for him... Don't think that because one computer got one guy bent it is wrong for everyone... There is no computer or table that is always accurate for any diver for any dive... It's about finding your level and maintaining yourself phyicaly to stay within it (Ie, stay in shape or get in better shape, don't smoke, don't drink excessivly the night before diving, etc...). For me, I am comfortable with the Savant for my diving.

 

[jetblast00]

Originally posted by Uncle Pug
BTW it is really irresponsible diving to take a computer into deco mode when all of them (especially your conservative ones) tell you not to do that... they cannot be relied upon to get you out safely. That is really not a very conservative move but unfortunately that is the *thinking* of too many computer divers today. I'm not even going to go into all the reasons that is such a bad idea....

If you plan on getting into a deco situation you had better have more than a computer.... you need an understanding of staged decompression diving and a couple of good bottom timers and a good depth gauge as well as the skill to hit and stick deco stops.

I'll second that. I would never use my computer for deco diving, and would hope that no one else would either. If you're going to be doing decompression diving, you need to have a thorough (sp?) understanding of deco theory, the training, and the skills. Deco dives have to be fully planned and understood in advance, not 'on the fly' the way a computer will let you dive...