RDP vs eRDPml vs Dive Computer

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@XS-NRG: Why are you filling in "XTL" in your divelog?

You can certainly deduce an approximate pressure group for a given multi-level dive from your dive computer. If your computer happens to crap out during the surface interval, then you can simply revert to tables for subsequent dives. To figure out the pressure group from a given multi-level dive profile (conducted with your dive computer), use the method I explained in a previous post in this very thread. It's easy to do and doesn't require an expensive proprietary download cable.

Excerpt from Post #89 in this thread...

My example and thinking here actually stems from something I witnessed. In a span of 4 dives in January I watched 3 separate people have computer failures: one smacked onto something and stopped working, one failed to turn on upon entering the water (someone turned the auto-on feature OFF), and the last was a battery failure.

I understand you may have a technique for figuring out a pressure group but I think I'm not understanding it fully. For my working computer I suppose I might be able to figure one out but for the poor soul who's battery died then that trick clearly won't work and really that's all I'm filling the profile section out for. Total loss of functionality whatever the situation. If that happens all I know is where my SPG needle got pushed for my max depth and the time from my dive watch. At that point I have no other information so by writing XTL it's clearly obvious that even using tables for subsequent dives we have a NO-GO for launch. I personally am only interested in filling that section out on the boat between dives so that I know where I stand. If after one dive I'm XTL then I know the rest of the day will follow suit and that at any point if a failure occurs I'm done. It's just a simple way I chose to write it. I could scribble the whole box out if I want, I could color it red, purple or green or I could put a sticker with a skull and cross bones in it. Either way for me I know what it means and it really all equates to the same thing.
 
My example and thinking here actually stems from something I witnessed. In a span of 4 dives in January I watched 3 separate people have computer failures: one smacked onto something and stopped working, one failed to turn on upon entering the water (someone turned the auto-on feature OFF), and the last was a battery failure.
@XS-NRG: Dive computers fail for various reasons. It happens. I've only seen a couple of computer failures in over 13 years of diving and 300+ dives. Maybe my dive friends are just super-careful and take gear maintenance seriously. :idk:
I have seen a number of divers who weren't able to pair up their hoseless, air-integrated computers with the transmitter during pre-dive checks, but I wouldn't characterize that as an outright computer failure. The dive computer functionality still worked on the wrist units, and subsequent dives could be conducted with attachment of an analog SPG.
I understand you may have a technique for figuring out a pressure group but I think I'm not understanding it fully.
All the dive computers I've encountered allow a user to enter "Dive Plan" mode during a surface interval.
"Dive Plan" mode displays NDLs at specific depths if another dive were to be conducted at that moment.
FWIW, this is how most divers check to see whether the surface interval has been "long enough."
Basically, you just map the string of NDLs/depths from your dive computer onto the the NDLs/depths on your dive tables. This approximates a table pressure group for the vast majority of recreational diving.
I don't know what brand/model computer you have, but I'm quite certain that you can figure out how to do this.
For my working computer I suppose I might be able to figure one out but for the poor soul who's battery died then that trick clearly won't work and really that's all I'm filling the profile section out for. Total loss of functionality whatever the situation. If that happens all I know is where my SPG needle got pushed for my max depth and the time from my dive watch. At that point I have no other information so by writing XTL it's clearly obvious that even using tables for subsequent dives we have a NO-GO for launch. I personally am only interested in filling that section out on the boat between dives so that I know where I stand. If after one dive I'm XTL then I know the rest of the day will follow suit and that at any point if a failure occurs I'm done. It's just a simple way I chose to write it. I could scribble the whole box out if I want, I could color it red, purple or green or I could put a sticker with a skull and cross bones in it. Either way for me I know what it means and it really all equates to the same thing.
Why are you choosing to be so conservative? It's so straightforward to use tables as a backup. Just back out the pressure group from your dive computer immediately after surfacing. Then if your computer happened to die during the surface interval, you could switch over to tables + watch + depth gauge.
Of course, if your computer failed during the dive, you'd have to make some approximations about your nitrogen loading.
If that happened to me, I'd just get some info from my buddy's computer.
On destination dive vacations, where I'd hate to miss any diving due to a computer malfunction, I take a second computer.
 
3 separate people have computer failures:

one smacked onto something and stopped working,
Not a failure. Avoidable.

one failed to turn on upon entering the water (someone turned the auto-on feature OFF), Not a failure. Improper pre-dive prepation. Avoidable. Few computers have an option to disable 'auto-on'. If they do, then computer function needs to be part of a pre-dive safety check. Same applies if the computer is used in nitrox or gauge modes.

and the last was a battery failure. Not a 'computer' failure. Appropriate maintanence/observance and timely pro-active battery change makes it avoidable. Only happens if you ignore the battery meter for months on end.

The essence is that all 3 issues were ultimately avoidable. Most importantly, the later 2 issues were avoidable through the application of proper diving procedures and proactive kit maintenance.

for the poor soul who's battery died then that trick clearly won't work and really that's all I'm filling the profile section out for. Most computers that I've seen refuse to activate on a dive below a set minimum battery level. They still provide info for a while after reaching that min level. They also flash and beep and otherwise warn the diver for a long time before that level is reached.



On another note: has anyone tried cross-referencing a computer NDL reading against tables to formulate a pressure group? Say, if your computer died on a surface interval, but at the end of your last dive you knew you had 48 minutes NDL at 10m? Pull out a PADI table and find 48 minutes NDL on the 10m column. That'd be your end pressure group?
 
On another note: has anyone tried cross-referencing a computer NDL reading against tables to formulate a pressure group? Say, if your computer died on a surface interval, but at the end of your last dive you knew you had 48 minutes NDL at 10m? Pull out a PADI table and find 48 minutes NDL on the 10m column. That'd be your end pressure group?

PADI Wheel shows I was a "T" pressure group before any SI (using 48 min @40' as the known NDL) or "X" PG at 35' (again using 48 min @ 35') - sorry I don't have metric tables to specifically answer your inquiry....

edit: - this is significantly out on the tables since the normal NDL for 35' is 205 min & 140 min at 40' - likely should hang it up for the day....

....or an "H" PG on the NAUI tables.... (43 min AMDT / 87 min RNT @ 12m(40')

which is also significantly out there (130min max @ 12m(40'))
 
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......If you feel so inclined, you can certainly "back out" table-equivalent pressure groups from your dive computer. .....
Simply enter "dive plan" mode immediately after surfacing from a given dive.
You will see NDLs represented for various depths on subsequent dives. Take note of these numbers.
Cross-reference these numbers with the numbers on a dive table to come up with a pressure group.......
This method has some merit, BUT .... the results could be greatly affected by the type - and settings - of dive computer you are using and by which depth you are considering.

Here an example.

My last dive was last Saturday (it is raining today .... so no real diving for me :depressed:), I am at sea level and did not do any dive to elevation since a while.
So, in theory my PG should be always A - for every depth in the table (I am using PADI's table for this test).

It happens that I have here at home 4 dive computers and I will use them to figure out what is my "Equivalent Pressure Group" using the method above.
When I will be at the office I will try with few more dive computers (I have ~50 there :D)

Here are the results so far.

equivalent_pg.jpg

Again,
another case where the results are skewed by the computer being used instead of just considering the dive profile, that, IMHO, is what matters most.

Alberto (aka eDiver)
 
Interesting where RNT=0... take for example (and I am guessing) - computer #1 just might be a Mares Puck - it defaults to 99 minutes max.... they do however seem to "converge" with some additional depth.

It is more interesting where they say you are after a dive, and having some residual loading...
 
.....It is more interesting where they say you are after a dive, and having some residual loading...
Yup.
As far as I know, the 4 dive computers in this test did not dive in the past week (unless they went by themselves :D)
 
PADI Wheel shows I was a "T" pressure group before any SI (using 48 min @40' as the known NDL) or "X" PG at 35' (again using 48 min @ 35') - sorry I don't have metric tables to specifically answer your inquiry....

Yep, so in both cases you could plan repetitive dives on your tables. :D

The only requirement is to know what your NDL was at the time your computer failed. That's an issue of situational awareness. Divers should know what their NDL is, at any given time.
 
...//....The only requirement is to know what your NDL was at the time your computer failed. That's an issue of situational awareness. Divers should know what their NDL is, at any given time.

Yes, lots of surprises. Very DC dependent.

I often compare my trusty Uwatec puck to my insanely obtuse VR3. The NDL on the tech computer on "easy" dives was always way too short. -turns out to be nothing more than the VR3 making the "optional" safety stop mandatory. -Same amount of time, just lost the "optional" part.

In short, when my optional stop is upgraded "I'm in deco".

http://www.scubaboard.com/forums/ba...t-dive-tables-dive-computers.html#post5886192
 
@XS-NRG: Dive computers fail for various reasons. It happens. I've only seen a couple of computer failures in over 13 years of diving and 300+ dives. Maybe my dive friends are just super-careful and take gear maintenance seriously.
ne_nau.gif

Maybe they are and I am too. But how bout the people that don't own their own gear and use rental equipment. The auto-on example I mentioned was on rental gear used by a tourist. Andy, you are right that is avoidable. This whole subject really does come down to whether or not you own your own gear and also take care of it appropriately and also know how to actually use it vs the rental divers and/or table divers. Clearly you have much more control over situations if you own the computer yourself and have it serviced properly and at regular intervals. It really goes without saying.

All the dive computers I've encountered allow a user to enter "Dive Plan" mode during a surface interval.

I don't know what brand/model computer you have, but I'm quite certain that you can figure out how to do this.

I have a Suunto Zoop and yes I know what the dive plan mode is and how to get to it, I just don't see exactly how you are correlating between those NDLs and the PADI table pressure groups that's all. On the last 10 dives I did we would go down at least 70 ft and the max was 92 feet and would wind around reefs slowly working our way up. The dives were anywhere from 45-59 minutes long and by the time I was at 25 feet my computer actually stopped showing my No Deco time as it was so high it wasn't worth showing (something like 187 mins if I remember correctly).

It's so straightforward to use tables as a backup. Just back out the pressure group from your dive computer immediately after surfacing. Then if your computer happened to die during the surface interval, you could switch over to tables + watch + depth gauge.
Of course, if your computer failed during the dive, you'd have to make some approximations about your nitrogen loading.

Sure it is, again, once I fully see how you're getting your pressure group. Running just tables is easy.

If that happened to me, I'd just get some info from my buddy's computer.

What exactly are you getting from your buddies computer? Will the dive plan be accurate? What if your buddy was a few feet deeper than you the whole dive? Or shallower? The profile would be different. How can this be accurate? Isn't this why we're taught never to share a computer underwater??? If the plan mode and the info displayed is the same regardless of the dive then it wouldn't matter and your technique should work.


Why are you choosing to be so conservative?

Really? I'm surprised you even asked that. Conservatism is up to the individual and if you remember back to your OW class you'll remember that there are secondary factors. I happen to fall into a couple of those. Also (as mentioned earlier regarding dehydration) everyone is different, everyone will differ from day to day and every situation must be looked at on a case by case basis. If I know I'm doing 10 dives on a trip and I happen to miss 1 then big deal. Same applies to a live-a-board, you miss 1 dive on a week long trip, who cares. Sure you'll be pissed off you're missing one but in the grand scheme of things it really doesn't matter. I'd rather chill out and relax on the boat knowing I can dive another day than be air lifted to a HBOT chamber and screw up my whole holiday because I took it too far. If you choose not to be as conservative then go nuts, that's your decision. Why do I choose to be so conservative? Because I can, and because it's my choice.

On destination dive vacations, where I'd hate to miss any diving due to a computer malfunction, I take a second computer.

BINGO!!! I couldn't agree more!




The essence is that all 3 issues were ultimately avoidable. Most importantly, the later 2 issues were avoidable through the application of proper diving procedures and proactive kit maintenance.

Yup, I would agree with that. And sure they may not be outright failures, but rather the computer being rendered useless until the issue is rectified either on the boat or back at the shop etc.

Most computers that I've seen refuse to activate on a dive below a set minimum battery level. They still provide info for a while after reaching that min level. They also flash and beep and otherwise warn the diver for a long time before that level is reached.

Did not know that, and it's good to know. I wonder if my computer will do that. I don't remember seeing anything on that but I'll have to go look again now.


On another note: has anyone tried cross-referencing a computer NDL reading against tables to formulate a pressure group? Say, if your computer died on a surface interval, but at the end of your last dive you knew you had 48 minutes NDL at 10m? Pull out a PADI table and find 48 minutes NDL on the 10m column. That'd be your end pressure group?

How are you doing this exactly? I'm on imperial here so if I understand this correctly... 35 ft, my max NDL is 205 mins (Z Group), subtract the 48 mins left means my dive time would be 205-48 = 157 mins therefore 35 ft for 157 mins yields: X pressure group? Am I doing this correctly?
 

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