While much good information has been offered, Snow Dog, with what are you actually having trouble? Where do you find yourself getting stumped?
Learning PADI dive tables
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OP
bigsnowdog
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I am sorry, I did not mean the science behind the purpose of it was arbitrary, I just mean the chart manages to be a big abstraction; the structure of it is arbitrary. Not intuitive at all.
OP
bigsnowdog
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It is embarrassing to admit, but I would see it demonstrated, have it seem to make sense, and then not be able to hang onto all of the steps in my mind to do it again 20 minutes later. I had some success last night and will work on it again tonight.
rstofer
Contributor
I don't see them an 'not intuitive', they do just the most simple thing:
1) you dive and absorb nitrogen - Table 1 tells you how much you have gained. Look at how many ways you can get to pressure group F. 100' for 11 minutes or 50' for 24 minutes. Either way, you're in group F
2) you sit around and give up nitrogen - Table 2 tells you how much you have lost. If you start in group F, you will be in group A after 1:35 (1 hr, 35 minutes) or group C after 0:25
3) you still have too much nitrogen so you can't stay as long as Table 1 indicates - Table 3 gives the RNT and ANDL. For group C and a planned depth of 50', your Adjusted NDL is 63 minutes and your RNT is 17 minutes.
If you actually do the next dive for 23 minutes (actual bottom time), you would add 17 minutes of RNT when you re-enter Table 1. So 50' for 40 minutes is pressure group M. And so on...
All this means is that, while you can make a first dive to 60' for 55 minutes (PG=W), if you only SIT for 1:00 (PG=G) your 2d dive to 60' can only last 34 minutes because you still have 21 minutes of RNT. If you SIT for 2:00 then your ANDL is 41 minutes with 14 minutes of RNT. See if you get the same numbers.
You start on the left of the front side, find a rouded depth and rounded time. You look at the diagonal row of letters to get your pressure group. You move further to the right for some surface interval. The longer you sit, the lower your pressure group gets. After you decide how long to SIT (surface interval time), you move down to get your new pressure group. Now you flip the table over and use that new pressure group to evaluate the next dive given a maximum depth in the left column. For depth and letter group there are two numbers: the RNT and the ANDL.
You do the dive for a planned depth and you note how long you were down. To that time you add the RNT and after rounding both depth and time, you look back in Table 1 and to the right to get your new pressure group. Then you do the SIT, RNT/ANDL, Table 1 sequence until you run out of tanks.
NAUI has their tables all on one side. In that regard it is a little easier to use because you don't have to flip back and forth. It also has a dive profile template on the back for working through dives.
Richard
1) you dive and absorb nitrogen - Table 1 tells you how much you have gained. Look at how many ways you can get to pressure group F. 100' for 11 minutes or 50' for 24 minutes. Either way, you're in group F
2) you sit around and give up nitrogen - Table 2 tells you how much you have lost. If you start in group F, you will be in group A after 1:35 (1 hr, 35 minutes) or group C after 0:25
3) you still have too much nitrogen so you can't stay as long as Table 1 indicates - Table 3 gives the RNT and ANDL. For group C and a planned depth of 50', your Adjusted NDL is 63 minutes and your RNT is 17 minutes.
If you actually do the next dive for 23 minutes (actual bottom time), you would add 17 minutes of RNT when you re-enter Table 1. So 50' for 40 minutes is pressure group M. And so on...
All this means is that, while you can make a first dive to 60' for 55 minutes (PG=W), if you only SIT for 1:00 (PG=G) your 2d dive to 60' can only last 34 minutes because you still have 21 minutes of RNT. If you SIT for 2:00 then your ANDL is 41 minutes with 14 minutes of RNT. See if you get the same numbers.
You start on the left of the front side, find a rouded depth and rounded time. You look at the diagonal row of letters to get your pressure group. You move further to the right for some surface interval. The longer you sit, the lower your pressure group gets. After you decide how long to SIT (surface interval time), you move down to get your new pressure group. Now you flip the table over and use that new pressure group to evaluate the next dive given a maximum depth in the left column. For depth and letter group there are two numbers: the RNT and the ANDL.
You do the dive for a planned depth and you note how long you were down. To that time you add the RNT and after rounding both depth and time, you look back in Table 1 and to the right to get your new pressure group. Then you do the SIT, RNT/ANDL, Table 1 sequence until you run out of tanks.
NAUI has their tables all on one side. In that regard it is a little easier to use because you don't have to flip back and forth. It also has a dive profile template on the back for working through dives.
Richard
There are many different types of learners. Occasionally I’ve had students who seemed helped by this:
For single dives, use only Table One.
For multiple dives, the table isn’t rectangular, it’s circular. Use the arrows. You will start and end on Table One.
Example: for two dives, start on Table One, follow the arrows to Table Two, follow the arrows to Table Three, and follow the arrows back to Table One (1-2-3-1) – a full circle.
For three dives, it’s 1-2-3-1-2-3-1.
Exception: minimum surface interval problems.
As others have suggested, always draw a profile and fill in what you can from the question.
Some questions have you start part way through a sequence of dives. Some have you stop part way through. Look for clues like “a diver in pressure group F”. Carefully read the questions to see what they are asking.
best wishes,
k
For single dives, use only Table One.
For multiple dives, the table isn’t rectangular, it’s circular. Use the arrows. You will start and end on Table One.
Example: for two dives, start on Table One, follow the arrows to Table Two, follow the arrows to Table Three, and follow the arrows back to Table One (1-2-3-1) – a full circle.
For three dives, it’s 1-2-3-1-2-3-1.
Exception: minimum surface interval problems.
As others have suggested, always draw a profile and fill in what you can from the question.
Some questions have you start part way through a sequence of dives. Some have you stop part way through. Look for clues like “a diver in pressure group F”. Carefully read the questions to see what they are asking.
best wishes,
k
firstdive2005
Contributor
I feel your pain. I was 45 when I first saw these tables. It's not easy to get ahold of these at that age especially when math is not a strong suit.
I had trouble figuring them out as I kept hearing most dives aren't 'square'. They are multi-level usually and you mostly will 'rely' on your computer. These elements confused me to the reason behind the tables and what are they 'for'. As I have read earlier in these posts I was told it is about nitrogen loading and nitrogen offgassing. It is about time down there and time on surface and going back down. I needed to know how much nitrogen was loading into my tissues. As I likely would not dive too many 'square' dives, it was just nescessary to get the understanding of how it worked. I dont really know when it clicked but I just kept going over and over the easiest stuff. Over and over. I kept reading on gas loading trying to understand that stuff. Actuallly over a relatively short time it all blended together. There was a great sense of relief from the frustration that I could not put it together after just going through it with the instructor. I got good enough that I passed my OW. As soon as I started diving thats when it started to make the best sense. I dove with my computer but I always stayed close to the tables for backup. I would do to the plan as if it was a square dive. Then I did the nitrox specialty. This was now not so hard. As I read all the stuff previous, it makes great sense to me know, maybe some of their samples of how to read to tables might have helped me. But for sure I know repetitive work with them is what got me through. I know you will get there bud, give yourself a break. Your not alone in beginners frustration, just practice your a$$ off and it will get there for you.
I had trouble figuring them out as I kept hearing most dives aren't 'square'. They are multi-level usually and you mostly will 'rely' on your computer. These elements confused me to the reason behind the tables and what are they 'for'. As I have read earlier in these posts I was told it is about nitrogen loading and nitrogen offgassing. It is about time down there and time on surface and going back down. I needed to know how much nitrogen was loading into my tissues. As I likely would not dive too many 'square' dives, it was just nescessary to get the understanding of how it worked. I dont really know when it clicked but I just kept going over and over the easiest stuff. Over and over. I kept reading on gas loading trying to understand that stuff. Actuallly over a relatively short time it all blended together. There was a great sense of relief from the frustration that I could not put it together after just going through it with the instructor. I got good enough that I passed my OW. As soon as I started diving thats when it started to make the best sense. I dove with my computer but I always stayed close to the tables for backup. I would do to the plan as if it was a square dive. Then I did the nitrox specialty. This was now not so hard. As I read all the stuff previous, it makes great sense to me know, maybe some of their samples of how to read to tables might have helped me. But for sure I know repetitive work with them is what got me through. I know you will get there bud, give yourself a break. Your not alone in beginners frustration, just practice your a$$ off and it will get there for you.
I have new open water students this weekend doing confined water and academics. When learning the tables I ask students to draw the profiles and write the information as we work sample problems.
I think this helps in two ways: it breaks a problem down into simple steps and the process of seeing it on paper and using the chart let's them see a practical realtionship.
In one class I had an IDC canidate use an example of a credit card. You know you have a certain limit and can't exceed that without a penalty. This would be your depth and time.
You then have your surface interval. The longer you hold off using your credit card again the less your balance or residual nitrogen will be because you would make a payment.
And finally on the back if you fail to pay off your credit card at the end of each month you incur interest or residual nitrogen that you have to account for on each subsequent dive. Don't forget to drown the RAT; Residual(white number) +
Actual (blue is what you can do) = Total bottom time.
It actually gets much easier. Knowing how the tables work allows a person to have a better understanding of how a dive computer works and what it's actually showing you.
Montana Diver
Contributor
I would agree with downloading the Dive table tutor from Scubatoys. They will give you the key to open the program if you join their forum. I worked the tables until I was comfortable in knowing that I knew the steps needed to make the table work. It's certainly a little confusing in the beginning, however if you have the tutor, it will show you how to get the right answer. I also have the PADI eRDPML, that I used to check the RDP tables. This is a Multi-Level RDP calculator. When I took my written PADI, I used tables and checked with the eRDPML. It is a great tool since it breaks down the dive into 5 ft intervals. Certainly not a dive computer, but accurate as a dive table. Keep working, it will happen.
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Snow Dog -- Thanks for the answer as to your issues with the RDP. Me, I found, and continue to find, the tables hard to work in no small part because I keep thinking, but this isn't a real dive situation (i.e., I hardly ever dive a square profile). While I am required to demonstrate them and be able to assist students in their use, I do NOT use them myself.
And now with the eRDPml I'm forced to use another poorly designed tool, sigh. (Why couldn't they use a display that "old fogies" can read -- not to mention the poor font choices. Oh, and why couldn't they have put in a simple calculator function while they were at it?)
And now with the eRDPml I'm forced to use another poorly designed tool, sigh. (Why couldn't they use a display that "old fogies" can read -- not to mention the poor font choices. Oh, and why couldn't they have put in a simple calculator function while they were at it?)
halocline
Contributor
I don't think Snow Dog is particularly interested in or debating the value of the theory behind the tables, he just wants to know how to use them. Those are two completely different issues. A good way to learn how to use them is to have guided practice. You just have to work out problems with someone who both knows how to use the tables and is good at explaining the steps you take, and will leave out the theoretical discussions.
You can also try writing down the steps you take, sometimes this helps to remember what you have to do and in what order.
You can also try writing down the steps you take, sometimes this helps to remember what you have to do and in what order.
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