time during ascent to allow nitrogen offgassing before continuing your ascent or surfacing. – Precautionary Decompression Stop. This is a stop at five meters (15 feet) for three minutes as a safety precaution when you have not exceeded the Maximum Dive Time. You should perform such a stop at the end of every dive. It is also known as a Safety Stop. – Required Decompression Stop. This is the amount of time specified by the NAUI Dive Tables, that you must spend at five meters (15 feet) whenever you exceed the Maximum Dive Time. Other tables specify additional stop depths for deeper or longer dives. • Actual Dive Time (ADT). This is the elapsed time from the moment you begin your descent from the surface until the time you return to the surface. Time spent at your Safety Stop does not need to be included in the Actual Dive Time when determining your Letter Group. • Residual Nitrogen. This is the excess nitrogen remaining in your body from any dive or dives made before you have completely offgassed. • Letter Group Designation. This letter symbol identifies the amount of residual nitrogen you have in your system. The closer the letter is to the beginning of the alphabet, the less residual nitrogen you have in your body. • Surface Interval Time (SIT). This is the time spent on the surface between dives. During this time, your body is eliminating excess nitrogen. Your Letter Group will change and move closer to the beginning of the alphabet, depending on how long you are on the surface. • Repetitive Dive. This is any dive that you make before you have completely offgassed from any previous dive or dives. • Residual Nitrogen Time (RNT). This is the amount of time you must consider as already having been spent at a given depth for a planned repetitive dive. This time is based on the residual nitrogen remaining in your body from a previous dive or dives. • Adjusted Maximum Dive Time (AMDT). This is the Maximum Dive Time minus the Residual Nitrogen Time for a repetitive dive to a given depth. • Total Nitrogen Time (TNT). This is the sum of your Residual Nitrogen Time and your Actual Dive Time following a repetitive dive. You use this total to obtain your new Letter Group at the end of the dive. Dive Table Rules You must understand the following NAUI Dive Table rules completely. Similar rules will apply to any new set of dive tables or dive computer that you might use to calculate your dive times. • Ascend no faster than 9 meters (30 feet) per minute. This is 0.3 meters (1 foot) every two seconds. You need a timing device and a depth gauge (or a dive computer) to measure your rate of ascent. This rate will seem quite slow to you. • Use the exact or the next greater number listed in the table for your depth. If you exceed a number in the table, use the next greater number. The depths in the table range from 12 meters (40 feet) to 40 meters (130 feet) and increase in increments of 3 meters (10 feet). For example, you round a dive to 13 meters (43 feet) up to a 15-meter (50-foot) dive. • Use the exact or the next greater number listed in the table for your time. If you exceed a number in the table, use the next greater number. The times range from 5 minutes to 130 minutes. For example, you round a dive to 15 meters (50 feet) for 41 minutes up to 50 minutes. • Use the deepest depth you reached during your dive to determine the dive schedule for your dive. For example, if you do a dive to 18 meters (60 feet), but spend most of the time at 12 meters (40 feet), you must consider the dive to be an 18 meter (60 foot) dive. • Always make your deepest dive first when making a series of dives. Plan each of your repetitive dives to a shallower depth than your previous dive. This might allow you to offgas nitrogen on NAUI Scuba Diver 128 Decompression, Dive Tables, and Dive Computers
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