During Chapter 5 you learned that decompression sickness can occur during ascent if your tissues and bloodstream contain too much nitrogen. The amount of nitrogen you ingas during a dive depends on several factors, with depth and dive time having the most significant influence.

Before you dive, it's important to review your dive tables or computer to verify that a planned depth and dive time will allow you to ascend without developing decompression sickness. If the planned dive exceeds the maximum limit, you'll need to reduce your maximum depth or dive time to keep the dive within safe limits. This chapter covers the procedures and rules for using your dive tables and computers to make these calculations.

Note: Specific terms, dive time limits, table features, and general table design vary between certification agencies. For this reason, the information presented by your instructor may differ slightly from what's presented in this chapter. Your instructor will highlight any significant differences during your classroom sessions.