In this section we explain dive tables and go through specific examples of repetitive dives, using both the PADI and the NAUI tables.
Dive tables are used to determine how long you can safely stay under water at a given depth, both for the initial dive and for subsequent dives. 
To many aspiring scuba divers, Dive Tables are scary. It seems inconceivable that they'd ever understand them, let alone become proficient in using them. And truth be told, dive tables -- called "Recreational Dive Planners" by PADI and just "Dive Tables" by NAUI -- do look complicated and intimidating with their tables and charts and unfamiliar terminology.
Even the supposedly friendly PADI recreational dive planner that every student must understand before s/he successfully completes the PADI Open Water Scuba Diver course and gets the certification card contains over a thousand numbers on both sides of a small 5 x 7 inch plastic card.
NAUI uses different dive tables, with all tables being on the same side (see the NAUI table above, and click on it to see a larger copy), but you're still dealing with well over 400 numbers. And there are other formats as well.
What's especially frustrating is that all dive tables do essentially the same thing, just not exactly the same way (and often with surprisingly different results). So the NAUI tables are a bit different from the PADI tables, and they use different definitions and acronyms -- just enough to throw you off. It's like driving a car where the gas is on the left and the brake on the right, and one calls the gas "accelerator" and the other "velocity increasing accentuator". My suggestion is to use and understand one set of tables and stick with them.
