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

[emttim]

Because different schools/scuba systems teach different tables. I have both PADI and SSI tables, and those two are completely different (SSI is more conservative in time allowed, and has fewer pressure groups). I don't know what other systems teach, but I presume there's quite a lot of different tables and pressure group values out there...

Also, if you already use a computer the whole point of the pressure group/tables is to give you a conservative limit that you can deal with when your computer breaks. So it's almost useless to have your computer give you the pressure group information when it's working... and it can't do it when it's not.

Finally, as was mentioned previously, even if everyone used the PADI table, and computers gave you the pressure group info according to the table, you will discover that a large chunk of the time the computer would just say something like 'pressure group INVALID', since computer dives almost always go beyond the limits of the tables.

Hmm, so then what's the generally accepted rule with dive computers so you avoid chancing a hit? Stay within the "yellow" bar or below on your nitrogen uptake according to your computer?

I like the idea of just assuming pressure group Z according to PADI tables (if a PADI diver) if you really want to use one since as Charlie said, if you're doing no deco diving and your dive computer says you still have bottom time left, then Z is a conservative assumption so you should be ok by doing that.

 

[reefduffer]

The computer is a relatively new (about 20 dives) addition, and I'm still < 100 dives total. I go through the PG calculation expecting that it will sometimes show me to be bent based on the use of max depth, because I'm curious about how often and how much. I'd like to get a sense, eventually more intuitive, of how much extra bottom time the computer gives me based on my typical profiles, or even the occasional atypical-for-me dive.

I suppose part of it would be understanding how to recover from computer death mid-trip, but there's also a desire to relate the magical-opaque ND time on the computer screen to my dive education and time/depth measurements. As I do it, I wonder why, answer myself as I've answered you, and think that maybe eventually I'll stop, but not yet.

 

[Blackwood]

Before you rest on that statement download this PDF from Rubicon and look at PDF Page Numbers 110 (bottom) and 197+.

Personally, I don't believe that pressure groups are needed in order to get a diver out of or back in the water following a computer failure.

In any case, that wasn't the point of my post. I was replying to this:

I understand that it is still good to know how to do it in case your computer fails, but as a general rule do you still do the calculations and note them in your log book?

It seems that the OP is asking if I (the "you" to which he was referring [/self centered post]) note pressure groups in my log book outside of using them to account for a computer failure.

To me, a log should contain data that may be useful to review in the future. Pressure groups figured from fictitious profiles are not.

Hmm, so then what's the generally accepted rule with dive computers so you avoid chancing a hit?

Don't breathe compressed gas.

 

[Cajuncru Diver]

Agreed Blckwood. I do not post pressure groups in my dive log as they do not provide worthwhile information

 

[stairman]

I dont even bother with tables anymore.Usually after the 2nd dive Im bent .I use two computers and carry deco tables in a thigh pouch where my spare mask rides.My profiles are too up and down to go by the deepest depth reached.

 

[hudson]

Hmm, so then what's the generally accepted rule with dive computers so you avoid chancing a hit? Stay within the "yellow" bar or below on your nitrogen uptake according to your computer?

You can't avoid it entirely, but to minimize, with Pelagic line of computers which are fairly liberal, yes. The equivalent with other more conservative computers (Mares, Suunto etc) would be a safety margin of a few minutes of NDL time before you ascend and in either case not to ride your NDL (max out at depth, ascend till you get credit, max out again). You should also use several stops from half-depth onwards - see several threads on deep stops.

 

[emttim]

Don't breathe compressed gas.

Real helpful smartass. I meant reasonably avoid the chance of a hit, not avoid it altogether since there's always inherent risks in diving just like anything else.

You can't avoid it entirely, but to minimize, with Pelagic line of computers which are fairly liberal, yes. The equivalent with other more conservative computers (Mares, Suunto etc) would be a safety margin of a few minutes of NDL time before you ascend and in either case not to ride your NDL (max out at depth, ascend till you get credit, max out again). You should also use several stops from half-depth onwards - see several threads on deep stops.

Fair enough, this is more along the line of what I was looking for. Out of curiosity, how liberal or conservative are Oceanic computers? I ask this because my buddy does dive a Mares but I dive a VEO-250 myself.

 

[Thalassamania]

Personally, I don't believe that pressure groups are needed in order to get a diver out of or back in the water following a computer failure.

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

 

[yyidus]

Fair enough, this is more along the line of what I was looking for. Out of curiosity, how liberal or conservative are Oceanic computers? I ask this because my buddy does dive a Mares but I dive a VEO-250 myself.

I think that depends on the model of Oceanic. The VT3 I have is actually a Pellagic computer (same as the Aeris V3). It's very liberal compared to most other recreational diving computers. However, you can modify its settings (more easily done via the computer interface). You can lower the PO2 threshold, and the nitrogen bar limit, to give you less diving time at less exposure. It also doesn't do 'deep stops' (although you can always do those youself).

 

[emttim]

I think that depends on the model of Oceanic. The VT3 I have is actually a Pellagic computer (same as the Aeris V3). It's very liberal compared to most other recreational diving computers. However, you can modify its settings (more easily done via the computer interface). You can lower the PO2 threshold, and the nitrogen bar limit, to give you less diving time at less exposure. It also doesn't do 'deep stops' (although you can always do those youself).

Right, and I have done that, I have my PO2 threshold set at 1.4 and my nitrogen at 4.0 ata respectively, I'm just a firm believer of staying out of the red zone for anything (always seemed like a safe bet) so just wondering if that holds true for dive computers' nitrogen levels or if perhaps that's a little too overzealous, and just staying within NDLs according to the computer would be a better way to go about it.

I'm definitely interested to know how to handle the computer thing because I have a liveaboard reserved for September and while I don't want to unnecessarily risk DCS, I don't want to get screwed out of dive time either, so I'm trying to walk a fine line by knowing how I should avoid both.