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Learning PADI dive tables

Discussion in 'New Divers and Those Considering Diving' started by bigsnowdog, Feb 16, 2009.

  1. bigsnowdog

    bigsnowdog Nassau Grouper

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    I am having a hard time learning the PADI dive tables. There seems to be nothing intuitive about it, as it is just an arbitrary construct. Is there any material on the web that offers a useful explanation regarding how to learn to use it?

    Thank you.
     
  2. fisheater

    fisheater Divemaster Candidate

    # of Dives: 200 - 499
    Location: Sebastopol, CA
    4,390
    946
    113
    It's not arbitrary. The numbers are based upon a rather complicated mathematical model of how our bodies react to increased and decreased pressures of nitrogen.

    I recommend that you check out the "table tutor" software that is available for FREE from ScubaToys (Scuba Gear Scuba Diving Equipment Discount dive gear Snorkeling Equipment and Wetsuits Cheap online).

    Also, carefully read the pamphlet that came with the PADI Recreational Dive Planner.

    Of course, there's always (or should be) your instructor! Ask for help.

    Lastly, if you want to read up on decompression theory and the creation of the Recreational Dive Planner (and other dive tables), there is a very good treatment of the subject in the PADI Encyclopedia of Recreational Diving (available through your LDS).
     
  3. Colliam7

    Colliam7 Tech Instructor Staff Member

    # of Dives: 1,000 - 2,499
    Location: Hillsborough, NC
    3,510
    1,122
    113
    The tables allow you to estimate your nitrogen load at the end of a dive (represented as a 'Pressure Group') - the deeper you go and/or the longer you stay, the greater the nitrogen load.. The tables then allow you to estimate the remaining nitrogen load after a surface interval (also represented as a 'Pressure Group'), then determine what effect that residual nitrogen load has on your bottom time on the next dive (the adjusted NDL). The values are not arbitrary, but they are not necessarily algebraically intuitive. Are there specific questions that you have about the tables, which might allow u to provide a more focused and informative response?
     
  4. CamG

    CamG Divemaster Candidate

    # of Dives: 500 - 999
    Location: Geneva Indiana
    1,798
    275
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    Greetings Snow Dog and welcome to SB! Others have covered a lot of the facts, I found the pink Padi guide to be the most helpful. They give you step by step directions to follow with examples. I worked the tables with their examples then plugged my own numbers in. It takes a while to get it down but with some practice and guidance from your instructor it gets easier.
    The more you use the tables the more familiar they will become. No worries, I have not tried the links but practice is practice and I am sure you will master it in the end.
    This section of the academics usually takes 30 - 45 minutes, we make sure everyone understands how to work the tables. PS. There is important information actually printed on the slate itself! I learned this after I used a pair of glasses for assisting in the OW academics. I wish I was kidding it is printed very very small on the slate and it is on the test! Hint...Hint! i am confident you will do well, just study and be prepared!
    Good luck and keep us posted on your progress!
    CamG Keep....diving....keep training....keep learning!
     
  5. DBailey

    DBailey Instructor, Scuba

    # of Dives:
    Location: Wrigley Field, Chicago
    746
    58
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    1. Did you read the little pink and grey booklet that came in the crew pack? Don't skip ahead just read it and follow along.

    2. The plastic card is three tables and fine print all combined in one. You will only be using one part of the plastic card at a time. Don't let the other sections throw you off.

    3. The word problems will usually give you four or five pieces of information. Draw the dive profile and put the information in the correct spots. You will use two piece of the given information to determine another piece. With that piece you will then apply it to another piece of given information to get another. It is all rather linear.

    4. Ask questions.
     
  6. RonFrank

    RonFrank Solo Diver

    # of Dives: 200 - 499
    Location: Conifer, CO
    9,106
    344
    0
    Understanding the dive tables, and the theory behind them is important. Unfortunately unless one does flat profiles, most folks use dive computers in place of the dive tables. Computers base their calculations on the tables, however they calculate nitrogen load based on actual depth during a dive rather than flat profile, and the rounding that goes into using the tables.

    I'm not suggesting that you don't learn them. It is important that you are proficient in using them. However most recreational divers follow their computers rather than rely on dive tables. Where understanding the dive tables comes into play is as a reality check when you are diving. If you know your NDL at 100 feet is 20 minutes, and your computer says your NDL is 40 minutes, than something is wrong! :D

    I dive two computers for that very reason. They generally agree (both are Aeris), but if one fails or floods, I have a backup.
     
  7. Doc

    Doc Was RoatanMan

    # of Dives:
    Location: Chicago & O'Hare heading thru TSA 5x per year with
    9,229
    1,892
    113
    I'll take your question in it's literal extreme.

    Such similar style "calculators" were very common in engineering for many years. Also in engineering, we see circular computers that are very mission specific.

    Simple wheel devices were used by graphic artists to compute what % of image reduction you will need to make a 16" picture into a 10" picture.

    Cubic Yards of concrete had similar devices. There must have been hundreds of different such gizmos.

    Before electronic calculators, we all learned how to do math on slide rules (slip sticks). Slide Rules were very expensive highly machined metallic instruments that served only to align finely printed numbers on moving surfaces. (You could look at a PADI wheel and describe it that way)

    That PADI wheel is also an invention that arrived a bit too late to be of any real use. Much derided as it is, it still is a mechanical visual demonstration of how multi-level diving can affect your diving.

    Remember, the standard card tables only take into account your maximum depth and figure everything from there. This was because they were derived from sending healthy young fat-free Navy divers to a pre-set depth, working on a project, then hauling them back up. There was simply no need or research in "multi-level" diving, dives where you go up and down and poking around. We started dive manuals for civilian use by utilizing Navy tables. It was all we had.

    As an electronic calculator is to math, The eRDP is to dive tables.

    Your dive computer has these dive tables in its brain, and it has also been taught to interpret your depth moment by moment and extrapolate for those known numbers.

    Learning how the tables work is integral to your understanding of Nitrogen loading. Learning to work the tables is a different deal.
     
  8. rstofer

    rstofer Loggerhead Turtle

    # of Dives: 100 - 199
    Location: Northern California
    2,199
    1
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    You will revisit the tables in great detail when you do the Nitrox course.

    Looking at dive tables from 10,000 feet up, they do the following:

    1) For a given maximum depth (rounded up) for a certain time (rounded up), the table gives you an indication of your nitrogen uptake in terms of a Pressure Group which is a simple alphabetic letter, A-Z. This is Table 1 on the left side of the front of the RDP.

    2) Given a nitrogen load (Pressure Group) resulting from a dive, Table 2 shows how that load is reduced over time by sitting on the surface (SIT - Surface Interval Time) and provides a resulting Pressure Group.

    3) Table 3 (on the back side) takes the Pressure Group after the SIT and shows how that modifies the NDL (No Decompression Limit) for a subsequent dive. It does this by providing, for the various depths, two numbers: First, the new Adjusted NDL (ANDL) and, second, the RNT (Residual Nitrogen time) You will note that the ANDL plus the RNT is exactly equal to the NDL for the same depth from Table 1.

    The important part to remember is that the RNT (Residual Nitrogen Time) for a given depth is added to the Actual Bottom Time (ABT) from your watch to get the Total Bottom Time (TBT) which is used to get a repetitive Pressure Group from Table 1 including the usual rounding upward for depth and time. RNT is time you have already accumulated for a dive to a specific depth before you ever get wet. It is as though you have already been there for RNT number of minutes. This is a very important number and an important concept.

    When I used tables, I would write the ANDLs for the various depths on my slate so that I could figure out, while underwater, given my maximum depth for the current dive, how long before I had to surface. I could just look at my depth gauge (actually, the maximum depth needle), ANDL slate and bottom timer to determine when the dive was over.

    This Table 1 -> Table 2 -> Table 3 -> Table 1 -> ... process is repeated over and over. Thus the idea of repetitive dives.

    The eRDP (calculator) and eRDP-ML (multi-level) will give you the same information including new Adjusted NDLs. Unfortunately, it does NOT give you RNT and that is a shame. Especially since the test has an RNT question (so I have been told). RNT is an important number to keep in mind. It's loss will be missed.

    Richard
     
    Last edited: Feb 17, 2009
  9. don Francisco

    don Francisco Manta Ray

    # of Dives: 500 - 999
    Location: Metro New York
    993
    3
    0
    Most people that have trouble using the tables do so because they psyche themselves out. They look at this piece of plastic with all these numbers and say to themselves "it's math, and complicated" and suddenly - poof - it is.

    Ironically these same people have no problem using simple calculators. Maybe if they knew what went on inside they'd freak out and go back to the pencil, but that's not the case. Electronic calculators are nice familiar little boxes with numbers and a screen, and they're so easy to use. Enter your data, and up pops the answer.

    So ask yourself if you'd be capable of entering basic data such as depth and time into a hand calculator. If the answer is "yes, of course" you can use the tables. Because despite what they look like they are nothing but a pre-programmed calculator for estimating nitrogen load in your body after a dive.

    Simply put the tables are a graphical calculator and you use them the same way as any other calculator except that instead of pushing a button, you input the first bit of data by putting your finger on it, and the second bit by finding it on the other scale, and running your finger down or across to the corresponding line, your finger is now on the answer. It's that simple.

    If you clear your mind of the idea that it's complicated, and follow the instructions step by step, you'll find that the tables are pretty simple devices after all, and their batteries never need replacement.
     
  10. knotical

    knotical perpetual student Staff Member

    # of Dives: 1,000 - 2,499
    Location: Ka'u
    5,747
    809
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    As others have said, work your way through the booklet a few times. If you still don’t get it, an option is to ask your instructor about the ERDP that RoatanMan mentioned. Knew of one student who struggled with the tables, even after working through the booklet several times. She picked up the ERDP quickly and said it helped her learn the tables afterwards. Also, standards now allow the ERDP to be used instead of tables.
     

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