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dive. Follow the same row as Dive One to the right and read your permitted maximum depth and MDT in the columns for Dive Two. Dive Two may be shallower but cannot exceed the depth and MDT on the same row as Dive One. If a third dive is permitted, follow the same procedure for Dive Three to find your maximum depth and MDT in the Dive Three columns (figure 5-21). Additional details, such as the rules for flying after Chapter 5- Decompression, Dive Tables, and Dive Computers diving or accidentally exceeding the MDT, are printed on the reverse of each table. The NAUI RGBM tables require no calculations for Letter Group or Residual Nitrogen Time. The sea level table may be used for up to three dives per 12-hour day (two dives per day for altitude table dives). If you plan on doing more dives than that, you cannot use the RGBM recreational dive tables. You will have to use a dive computer or the regular NAUI dive tables. USING DIVE COMPUTERS There are three ways to determine how long you can dive and then ascend within the dive time limits. We have already discussed two. The third and easiest way is to use a dive computer (figure 5-22). This is also the most expensive way to monitor your bottom times, but it is used by more divers every day. Different body tissues absorb and release nitrogen at different rates. Mathematical models (programs) considering theoretical tissues have been developed to estimate ingassing and outgassing from various tissues. Dive computers with these mathematical models continuously sample depth and time and calculate the amount of nitrogen in each tissue model for any given moment. The computer uses this information to determine the time limits for the current depth and displays it for the diver. Remember that both dive tables and dive computers are only theoretical models of what happens in the human body. No presently available method of calculating your excess nitrogen accurately accounts for your individual age, body type, level of fitness, fatigue, drug or alcohol use, and so on. Dive tables provide time limits in increments of 3 meters (10 feet) of depth and assume that you spend the entire dive at the deepest depth. This is one disadvantage to the use of the tables as compared to a dive computer. A dive computer might calculate both ingassing and offgassing in increments as little as 0.3 meters (1 foot) for the depth at which you are diving. The computer constantly recalculates as your depth changes during your dive. A dive computer does not count all of your dive time as having occurred at your deepest depth. When Decompression, Dive Tables, and Dive Computers 143 FIGURE 5-21. RGBM TABLE FOR AIR FROM SEA LEVEL TO 2000FT/610M. FIGURE 5-22. THERE ARE MANY DIFFERENT TYPES OF DIVE COMPUTERS.


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