RDP vs eRDPml vs Dive Computer

[XS-NRG]

During my OW class we only dove with RDP and the few of us that had the eRDPml used those (however we were at altitude too - 5000 ft). After getting that I went to Australia to get my AOW and right off the hop I was using a computer and after 2 dives decided to buy one. As far as my log goes I have a fairly involved log that I actually made myself that gives more info and more room for stuff like Altitude Diving (which I will be doing the most) and Nitrox info such as my EAD and dive PPO2 and daily O2 % as a cumulative total. I fill this in religiously after every dive for a number of reasons:
1 - I know when and where I was
2 - I know certain situations (cold water, what wetsuit strength, current etc)
3 - SAC rate and air consumption etc
4 - Easy Altitude calculations (with enough room to work it all out)
5 - MOST IMPORTANT - Calculate bottom time and depth so I know if I can dive again should my computer fail.

The 5th part is the most important and because I multi-level computer dive every time my ending pressure groups are always way off the RDP and eRDPml scales but in fact I'm still being quite conservative. When it comes to the profile portion of the log I'll fill in my max depth and any associated EAD (Nitrox) and/or theoretical depths (altitude) plus my safety stop but pressure groups almost always end up reading "XTL" (eXceeds Table Limit) meaning that if the computer failed one look at the log says "sorry, no more diving today".

Bottom line, forget the profile if you are computer diving, the computer is more accurate but do know how to fill it in in case your computer gives up the ghost.

 

[lowviz]

...//....Bottom line, forget the profile if you are computer diving, the computer is more accurate ...//....

Your opinion. My opinion:

Blind faith and a statement of "fact".

The computer, tables, or anything else for that matter, all draw a sharp "all is fine/ you are gonna get hurt" line through a fuzzy gray area that is supposed to apply to all divers. Know of a person (in my LDS) who got bent a day after a day of hard partying, -dehydrated. In his particular case, on that particular day, tables would have been more accurate.

Tables don't guarantee safety, but they <<usually>> provide a bit of a safety margin over a DC. That margin is quite variable depending on time and depth. I like to both use tables for some dive plans and compare them to my DC's suggestions for other dive plans, nothing more.


The deco clock ticks the fastest at the very worst of times and you never really know what time it is until it is too late for you. Not all divers on the same dive are on the same clock.

 

[XS-NRG]

Your opinion. My opinion:

Blind faith and a statement of "fact".

The computer, tables, or anything else for that matter, all draw a sharp "all is fine/ you are gonna get hurt" line through a fuzzy gray area that is supposed to apply to all divers. Know of a person (in my LDS) who got bent a day after a day of hard partying, -dehydrated. In his particular case, on that particular day, tables would have been more accurate.

Tables don't guarantee safety, but they <<usually>> provide a bit of a safety margin over a DC. That margin is quite variable depending on time and depth. I like to both use tables for some dive plans and compare them to my DC's suggestions for other dive plans, nothing more.


The deco clock ticks the fastest at the very worst of times and you never really know what time it is until it is too late for you. Not all divers on the same dive are on the same clock.

When I said that I meant more for after the dive when figuring out your ending pressure group etc. Forget trying to draw out the profile at that point unless you decided on a table dive in the first place and stuck to it no matter what your computer said. The computer will be more accurate though as you hardly ever square profile dive (not to say that it isn't done) and if you do exceed your table limit then you can't really put anything in the spot for end pressure group etc. If you want to draw out a profile for multi-level and have recorded depths and time at depth throughout the dive then you can probably work it out in the end. Once I get the cable for my computer I'll likely end up printing the actual profile out

As far as your dehydration example, sure tables could have been better, but they aren't necessarily more accurate but certainly are more conservative. Who's to say that even if he dove with tables he wouldn't have been bent? Obviously it's rhetorical and hearsay.

My statement wasn't a blanket statement, please don't take it that way, obviously there are many other factors involved: age, weight, fitness, cold water etc. Sure none of these systems of checks and balances are fool proof, everyone is different and will differ from day to day too.

 

[lowviz]

You make a better case if you replace the word "accurate" with the word "precise". Accuracy and precision - Wikipedia, the free encyclopedia

I consider dive computers to be exquisitely precise, but not very accurate as the target (you) changes from day to day and dive to dive. It is instructive to see how much more conservative the "table of your choice" wants the "average" diver to be for the same dive. A big difference means that I am going to look into this profile a bit further. It isn't always the fastest compartment that calls the dive, the difference can be illuminating...

-glad that you care enough to think about this and post.

 

[DiveNav]

You make a better case if you replace the word "accurate" with the word "precise". ....

In our classes we say:
- tables = rough estimate
- computer = detailed estimate

at the end of the day ... they are still estimates

Alberto (aka eDiver)

 

[Bubbletrubble]

When it comes to the profile portion of the log I'll fill in my max depth and any associated EAD (Nitrox) and/or theoretical depths (altitude) plus my safety stop but pressure groups almost always end up reading "XTL" (eXceeds Table Limit) meaning that if the computer failed one look at the log says "sorry, no more diving today".

When I said that I meant more for after the dive when figuring out your ending pressure group etc. Forget trying to draw out the profile at that point unless you decided on a table dive in the first place and stuck to it no matter what your computer said. The computer will be more accurate though as you hardly ever square profile dive (not to say that it isn't done) and if you do exceed your table limit then you can't really put anything in the spot for end pressure group etc. If you want to draw out a profile for multi-level and have recorded depths and time at depth throughout the dive then you can probably work it out in the end. Once I get the cable for my computer I'll likely end up printing the actual profile out

@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...

If you feel so inclined, you can certainly "back out" table-equivalent pressure groups from your dive computer. No expensive software programs or mental gymnastics are needed.
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.

For example, let's say you just conducted a computer-based, multi-level dive to a max-depth of 70 fsw with a run time of 60 minutes.
(N.B.: The standard PADI RDP tables wouldn't allow such a dive since a square profile is assumed.)
Upon exiting the water, you enter "dive plan" mode and see that you are given the following NDLs/depths: 67 min at 40 fsw, 28 min at 50 fsw, 14 min at 60 fsw, and 6 min at 70 fsw.
If you reference the back side of your PADI tables, you'll see that this series of NDLs/depths is roughly equivalent to pressure group Q.
Theoretically, you could use this pressure group to approximate the nitrogen loading "credit" you would earn during the surface interval. You would note that after a one hour surface interval, your pressure group would be F.

 

[beaverdivers]

Agreed 100%. Most Divemaster candidates I know struggle to pick that stuff up quickly.

We have been downloading, analyzing and using the Air integrated hoseless dive computer since the late 90'.

Our students have no problem grasping the concepts using this graphic representation on our 40" Sony Bravia in full color.

Isn't it more visual and meaningful than a group D diver?

Of course, we are teaching a lot of 5th graders.

Have you seen the TV show " Are you as smart as a 5th grader? "

 

[lowviz]

We have been downloading, analyzing and using the Air integrated hoseless dive computer since the late 90'.

Our students have no problem grasping the concepts using this graphic representation on our 40" Sony Bravia in full color.

Isn't it more visual and meaningful than a group D diver?

Of course, we are teaching a lot of 5th graders.

Have you seen the TV show " Are you as smart as a 5th grader? "

Yeah, right. I finally lost it for you on this post, 40" Sony Bravia.


So you are going to tell me that your students can quantify their nitrogen loading on past dives? A careful re-read of your past posts can only lead me to believe that your students know only how to interpret what their DC is telling them at the moment, precious little more. Maybe even you don't understand...

Not my issue.
Bye.

 

[Bubbletrubble]

Our students have no problem grasping the concepts using this graphic representation on our 40" Sony Bravia in full color.

Yeah, right. I finally lost it for you on this post, 40" Sony Bravia.

I think it's quite possible that beaverdivers might also sell Sony TVs.

 

[lowviz]

We have been downloading, analyzing and using the Air integrated hoseless dive computer since the late 90'.

Our students have no problem grasping the concepts using this graphic representation on our 40" Sony Bravia in full color.

Isn't it more visual and meaningful than a group D diver?

Of course, we are teaching a lot of 5th graders.

Have you seen the TV show " Are you as smart as a 5th grader? "

-please explain "analyzing". -your specific reproducable procedure, not the meaning of the word...