Actually, it isn't a completely academic exercise. After a dive when I am doing another dive later in the day, I always use the planner on my computer to figure out my current post dive pressure group. While I am not doing this for logging purposes, I do it so that if I suffer a computer failure between dives, I can do my next dives with my brass and glass and charts, thus not ruining a nice Sunday afternoon at the beach. That makes it so you don't have to be 100% dependant on the computer.
Best way to calculate dive tables from a dive computer?
- Thread starter Scubaru_Steve
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Scubaru_Steve,
It is easy, only as long as your dives stay within the confines of the NDLs on the RDP (or eRDP), for your first dive and repetitive dives. If you are going to try to determine pressure groups, you have to use your maximum depth and time, just as with the RDP.
That being said, if you are diving the kind of profiles that will always be within the RDP and calculating pressure groups, you are really just using the computer as a depth gauge and timer.
It is easy, only as long as your dives stay within the confines of the NDLs on the RDP (or eRDP), for your first dive and repetitive dives. If you are going to try to determine pressure groups, you have to use your maximum depth and time, just as with the RDP.
That being said, if you are diving the kind of profiles that will always be within the RDP and calculating pressure groups, you are really just using the computer as a depth gauge and timer.
Buoyant1
Contributor
You're never going to have the same result between the tables and your computer?!?! If you used that confounded "wheel" you might get close, but the tables are all based on your deepest depth, and dive duration from a square dive profile! (even if you hit 50 feet for a SECOND and the rest of your dive is at 30 feet, you have to use 50 ft!)
I stopped playing with the tables once I realized that if I used the tables (properly) on some of the dives I've done, I'd be "bent"! (as someone else said; on paper) I log my dives into my book, with the dive time, and deepest depth, and DON'T figure them out with tables because there's really no tangible reason! (unless you just like playing with the tables to keep in practice)
Using the two dives I did at Dutch Springs this past Monday as an example, my first dive would have been off the charts! Deepest depth was 104, and the duration was 47 minutes. Looking at my tables using the dreaded "square profile" (I was diving 32% NITROX) I would need to sit out the rest of the day, and hit the chamber as a precaution! BUT I did a second dive of 63 feet for 52 minutes. Using "average" depths it becomes more realistic because obviously I DIDN'T do the entire dive at 104! (which is one tiny area out past the trolley and car... and only that deep because of the recent rains) I think the average depth for the first dive ended up about 60 ft.
But when we learned the tables, it was a "square profile" and that was it! Had I followed the tables, my dive would have been over before we hit the back of the island and the Cessna!
I think tables are good to know as contingency, and as you get deeper into this sport, and potentially get into serious dive planning, tables become your friend (as does decompression software) but the computer is your friend! Use it as the tool it is and don't worry about the tables for your log book!
I stopped playing with the tables once I realized that if I used the tables (properly) on some of the dives I've done, I'd be "bent"! (as someone else said; on paper) I log my dives into my book, with the dive time, and deepest depth, and DON'T figure them out with tables because there's really no tangible reason! (unless you just like playing with the tables to keep in practice)
Using the two dives I did at Dutch Springs this past Monday as an example, my first dive would have been off the charts! Deepest depth was 104, and the duration was 47 minutes. Looking at my tables using the dreaded "square profile" (I was diving 32% NITROX) I would need to sit out the rest of the day, and hit the chamber as a precaution! BUT I did a second dive of 63 feet for 52 minutes. Using "average" depths it becomes more realistic because obviously I DIDN'T do the entire dive at 104! (which is one tiny area out past the trolley and car... and only that deep because of the recent rains) I think the average depth for the first dive ended up about 60 ft.
But when we learned the tables, it was a "square profile" and that was it! Had I followed the tables, my dive would have been over before we hit the back of the island and the Cessna!
I think tables are good to know as contingency, and as you get deeper into this sport, and potentially get into serious dive planning, tables become your friend (as does decompression software) but the computer is your friend! Use it as the tool it is and don't worry about the tables for your log book!
OP
Scubaru_Steve
Contributor
Good point, I will be sure to fill in the depth and time, but leave the nitrogen levels and stuff empty. I know its a square profile and when I see my dive profile from the Cobra 3 its anything but square, I had hit 90' for about 1 min and the rest of the dive was at around 60'.
So where in that area of the Trolley does it hit 104'? I've been down there twice and my deepest depth was 91' and that was skimming the muck at the bottom. Also what is the heading on the old car? I hear its nothing spectacular to see but I think it be cool to venture out to look at.
Just out of pure interest, have you used the "planning" feature on your computer, recording what the NDL times are, and checking them "backwards" against the tables to see what pressure groups it equates to?
I use a computer and the aforementioned "confounded wheel", and can work through it somewhat close.... I like the utility of the wheel as a solid back-up or a good pre-dive planning tool.
No, it won't always work...... DiveNav's stuff (or other programs) kicks in then....
I use a computer and the aforementioned "confounded wheel", and can work through it somewhat close.... I like the utility of the wheel as a solid back-up or a good pre-dive planning tool.
No, it won't always work...... DiveNav's stuff (or other programs) kicks in then....
I frequently do that with my computer to make sure I can use my SPG as a backup. Its pretty simple. Get out of the water, go to your planning mode, find a depth that matches your particular chart, look at your max bottom time, and poof you have your pressure group. For instance if I go on a nice crazy sawtooth profile dive with my computer, and can't possible chart it without being paper bent, I simply go to, say 90ft as an example, if my planner says 13 mins then I back into my PADI chart and see that I am at pressure group "F." after that dive. Now when I take off my watch and somebody sets a big ole tank on it, smashing it to smitherines before my next dive, I can still spend the day diving on my chart.
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