In NAUI planning, the group letter is used to determine residual nitrogen time.

• A. The residual nitrogen time
• B. Buoyancy characteristics
• C. Visibility
• D. Tank fill

Answer: (A)

The group letter represents how much nitrogen you’re still carrying into the next dive from your previous dives and surface intervals. That labeling is used to determine residual nitrogen time, which is the portion of your next dive’s plan that accounts for that existing nitrogen load. When you plan the next dive, you look up the residual nitrogen time for the depth you intend to dive and add that time to your planned bottom time. This sum is checked against the no‑decompression limit for that depth to ensure you stay within safe limits. The bigger your residual nitrogen, the shorter your allowable bottom time becomes. If needed, you adjust by shortening the planned bottom time or increasing the surface interval. Other factors like buoyancy, visibility, or tank fill aren’t determined by the group letter.