surface interval inpressure group w or x

Question
QUESTION: what is minimum surface interval in pressure group w or x

ANSWER: Hi Alvin, I am a little unclear as to your question so I will answer it two ways.

I assume this is a PADI Recreational Dive Planner question so I will be referring to those tables.

The minimum surface interval for ANY pressure group is zero minutes.  However, I think what you were asking is what is the minimum SI to move from pressure group X to pressure group W.

If you read down the left column of the table to letter X; then read across to the surface interval numbers.  The first pair is 0:00 to 0:02.  Read down from that number and you read X again.  Thus a 2 minute SI would leave you in pressure group X still.

Keep reading across and you will see 0:03 to 0:05.  Read down and you will see letter W.  This means that you must have a minimum surface interval of 3 minutes to move from X to W.

As you should know, the pressure group letters are a representation of the amount of nitrogen present in your blood stream after breathing compressed air at depth.  You then use the letters to determine your adjusted no decompression time on subsequent repetitive dives.

Good luck and have fun diving, Jesse

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QUESTION: Thanks Jesse
I still would like to calculate how do you find surface intervals when you're not given specific times

ANSWER: OK, the second part of the answer I gave would be an example of how to determine the minimum surface interval to move from pressure group X to pressure group W.  As a further example, using the PADI dive tables, if you wanted to go from group X to group Q, reading across from the X row until you see the numbers of Q, you would read 0:23 and 0:26; thus the minimum interval is 23 minutes.

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QUESTION: Thanks Jessie
Sorry to burden you with these questions my instructor has no patients for someone that has not gotten the tables yet. If I was not left with only 2 open water dives for my open water cert I woulod bail on him. Is there any tips you can give me that I can become efficent with the charts.

Answer
Hi Alvin.  Understanding how to use the tables is a critical skill to ensure that you are able to dive safely and reduce the likelihood of decompression sickness.  As with all things, it will take practice for you to master the use of dive tables.  The wording of your previous questions leads me to believe that you need to go back to some fundamentals.

First, you should be able to clearly identify and define features of the tables and what it is that the tables are telling you.  Make sure that you can define all of the following:  depth, bottom time, pressure group, no decompression time, residual time, adjusted no decompression limit, surface interval, repetitive dive.

Now start with simple problems.  You should be able to readily determine what the no decompression limit is for a given depth. You also be able to readily determine the pressure group for a given depth and planned bottom time.  

Next you should be able to determine a new pressure group after a given surface interval.  Then you should be able to use the repetitive dive table to determine an adjusted no decompression limit and the residual time for a given depth, pressure group (from the first dive).

Finally you should be able to determine the pressure group for a repetitive dive.

In more advanced scenarios you can determine what a minimum surface interval would be for a repetitive dive to allow you to dive a particular depth for a given time.

Since you are paying for your dive training, you have the right to request from your instructor one on one training to help you master the tables.  In addition, if you are taking a PADI course, PADI offers alternatives to the tables such as an electronic Recreational Dive Planner (eRDP) that is like a calculator which you may find easier to use.

Best of luck, Jesse