Do you still calculate pressure groups if you use a computer?

[Blackwood]

How would you get a diver back into the water? I am curious what other approaches are out there.

Well, to be fair, I don't dive with either a computer or with traditional tables, so my comments may not fit the paradigm we're discussing. I'm just thinking "aloud" here, so bear with me.

In theory, most of the inert gases I have accumulated can be cleaned out (at least to some very small gradient) by diving. So an approach I would consider is to play it like an omitted or abbreviated deco scenario. That is to say: I'd go back down and do good deco (probably something like 1.5 or 2 times my standard schedule). Apply my personal SIT with some padding (so call it two hours), after which I'll dive as if I haven't been in the water for a week.

 

[Blackwood]

Real helpful smartass.

You're welcome.

Problem is, you are dealing with a bunch of different algorithms (well, most computers are bastardizations of buhlmann's work, but some use VPM and some use RGBM) which have been massaged by a legal team.

The red/green distinction is a little too arbitrary. And, in any case, deco isn't black and white like "one more minute and you're definitely screwed." Problem is, if you push your computer until it says "DECO," it will possibly give you a ridiculous set of instructions that, in my opinion, put you more at risk than your simple overstay of an artificial limit.

I've put a computer into 'deco mode' and had it instruct me to immediately ascend to 10 feet. Ignoring it, I've regained (in its 'mind') a lot of NDL by the time I hit 40 feet (some 1 ATM deeper than its "holy crap you're dead unless you go here" target).

I guess my thought is this: whatever method you adopt for figuring decompression, adopt it fully. Own it. Believe in it. Be it a table like PADI's RDP, be it a computer like the Vytec, be it software like V-Planner, or be it an 'on-the-fly' technique like Ratio Deco, believe in it.

"Staying in the green" is evidence that you don't trust the methodology, and if you don't trust it, you shouldn't be diving it, period.

 

[BarryNL]

I've put a computer into 'deco mode' and had it instruct me to immediately ascend to 10 feet. Ignoring it, I've regained (in its 'mind') a lot of NDL by the time I hit 40 feet (some 1 ATM deeper than its "holy crap you're dead unless you go here" target).

Are you sure you were reading it right? Most computers, when they hit deco, give you a "don't shallower than 10 feet" warning, but they don't tell you to immediately go there - they just give you the shallowest depth you can safely ascend to at that point.

 

[Blackwood]

Don't remember the model (it was an Oceanic), but I looked at the instructions afterwards and believe I was being instructed to ascend. Could be wrong.

The main thing that bugged me was that as soon as it went into 'deco mode' it hid the bottom time!

 

[muddiver]

How would you get a diver back into the water? I am curious what other approaches are out there.

I dive an Oceanic, that I thought was based on a conservitive caculation similar to the PADI table. I find that when I calc the tables after more than one dive I do best by using the U.S.N. tables, which are more liberal than the PADI table. Even if I blow the basic No "D" table I can always go into the Std. "D" on Air table and find a good landing point. 90% of the time my ascent, or safety stop is pretty close to the Std. "D" on Air table stops. If not, reference Blackwood's statement

I guess my thought is this: whatever method you adopt for figuring decompression, adopt it fully. Own it. Believe in it. Be it a table like PADI's RDP, be it a computer like the Vytec, be it software like V-Planner, or be it an 'on-the-fly' technique like Ratio Deco, believe in it.

, and I just call it a day.

 

[Thalassamania]

Well, to be fair, I don't dive with either a computer or with traditional tables, so my comments may not fit the paradigm we're discussing. I'm just thinking "aloud" here, so bear with me.

In theory, most of the inert gases I have accumulated can be cleaned out (at least to some very small gradient) by diving. So an approach I would consider is to play it like an omitted or abbreviated deco scenario. That is to say: I'd go back down and do good deco (probably something like 1.5 or 2 times my standard schedule). Apply my personal SIT with some padding (so call it two hours), after which I'll dive as if I haven't been in the water for a week.

Thanks for sharing, I need to mull that around a bit.

 

[emttim]

You're welcome.

Problem is, you are dealing with a bunch of different algorithms (well, most computers are bastardizations of buhlmann's work, but some use VPM and some use RGBM) which have been massaged by a legal team.

The red/green distinction is a little too arbitrary. And, in any case, deco isn't black and white like "one more minute and you're definitely screwed." Problem is, if you push your computer until it says "DECO," it will possibly give you a ridiculous set of instructions that, in my opinion, put you more at risk than your simple overstay of an artificial limit.

I've put a computer into 'deco mode' and had it instruct me to immediately ascend to 10 feet. Ignoring it, I've regained (in its 'mind') a lot of NDL by the time I hit 40 feet (some 1 ATM deeper than its "holy crap you're dead unless you go here" target).

I guess my thought is this: whatever method you adopt for figuring decompression, adopt it fully. Own it. Believe in it. Be it a table like PADI's RDP, be it a computer like the Vytec, be it software like V-Planner, or be it an 'on-the-fly' technique like Ratio Deco, believe in it.

"Staying in the green" is evidence that you don't trust the methodology, and if you don't trust it, you shouldn't be diving it, period.

Well, it's not that I don't trust the methodology per se, it's that I'm very objective-oriented in the sense that if a computer tells me I can do something, and I can't derive the same answer from say a series of mathematical formulas like I can for diving nitrox, then I'm inherently going to be wary of what the computer is saying since I have no way of proving to myself that it's right.

If you want to talk about using a method and believing in it, my preferred method would be linking my VEO-250 to my laptop, downloading my dive profile and getting as decent a pressure group calculation as I could from the Wheel. The problem? I don't have the data cable to hook my dive computer up to my laptop (and its 80 bucks last I checked), I don't have a Wheel, and I don't know how to use the Wheel in the first place.

Although come to think of it, technically I could still use the nitrox formulas to get as exact an EAD as possible and reduce rounding error by just using EANx21 since that's basically the same gas mix as air for all intents and purposes. I'll have to play around with it.

As far as I can tell though, for deco mode on Oceanic computers, I've owned two and both instruction manuals tell me that when you enter deco mode the ceiling is 10 feet, so it's not necessarily telling you to ascend to 10 feet but to go no shallower than that.

Are you sure you were reading it right? Most computers, when they hit deco, give you a "don't shallower than 10 feet" warning, but they don't tell you to immediately go there - they just give you the shallowest depth you can safely ascend to at that point.

This is what I inferred(sp?) from the instruction manuals for my VEO-100 & VEO-250. Ironically, because of the chance of a computer failure, when I switched to a VEO-250 wrist computer from my VEO-100 console computer, I left the VEO-100 on there, so I'm actually diving two computers on every dive because I figured having a backup isn't necessarily a bad thing. If one of my computers fail, it'll end up being a damn useful thing, for that matter.

 

[Saltwater Junky]

Re: OP question

I do. Just out of habit.

 

[Blackwood]

Well, it's not that I don't trust the methodology per se, it's that I'm very objective-oriented in the sense that if a computer tells me I can do something, and I can't derive the same answer from say a series of mathematical formulas like I can for diving nitrox, then I'm inherently going to be wary of what the computer is saying since I have no way of proving to myself that it's right.

You can. But who's to say that the series of formulas is right? Unlike the gas simple gas properties manipulated in basic nitrox calculations, deco is theoretical. No one really knows what causes gas to bubble. Your tables, the wheel, a computer, probably figure something like 1.58ATA gradient. But there's nothing hard and fast about it.

Why are you wary of the 'red zone' but not of the 'green zone'? It just seems to me that if you take exception to the numbers you're getting out of a computer, you shouldn't be using that computer.

As far as I can tell though, for deco mode on Oceanic computers, I've owned two and both instruction manuals tell me that when you enter deco mode the ceiling is 10 feet, so it's not necessarily telling you to ascend to 10 feet but to go no shallower than that.

Fair 'nuff. I was probably wrong, and that's beside the point anyway.

 

[Rhone Man]

Re: OP - I usually do, just for something to do during the safety stop. Keeps my brain active.

I don't think it would ever seriously be a backup for a failed computer, as I don't record my depth/time other than by computer, so I would be "guesstimating" anyhow if the computer failed.