What does the PADI Instructor Exam test on the RDP?

The PADI Instructor Exam written papers test three areas of RDP knowledge: decompression theory (how tables work and why), eRDPml operation (all four modes), and RDP Table calculations using Tables 1, 2, and 3. Candidates must correctly calculate pressure groups, surface interval credits, adjusted no-decompression limits, and total bottom times.

What is the difference between the RDP Table and the eRDPml?

The RDP Table is a printed three-table system used to plan dives manually. The eRDPml is the electronic version — it performs the same calculations automatically and adds two additional planning modes: Maximum Depth Mode and Multilevel Dive planning. Both tools use the same underlying algorithm and produce the same results for equivalent inputs.

What is decompression theory and why is it in the PADI IDC?

Decompression theory explains the physiological basis for dive tables — how nitrogen is absorbed by theoretical tissue compartments at different rates, why M-values define safe ascent limits, and how surface interval credit is calculated. PADI instructors need this knowledge to explain dive planning principles to students and to understand the rules they are teaching.

How do I use the PADI RDP Table for repetitive dives?

For a repetitive dive, use Table 1 to find the pressure group at the end of your first dive. Use the Surface Interval Credit Table to convert your surface interval into a new starting pressure group. Then use Table 2 to find the Residual Nitrogen Time (RNT) for your planned depth. Add RNT to your planned Actual Bottom Time (ABT) to get Total Bottom Time (TBT), and check TBT does not exceed the no-decompression limit for that depth in Table 1.

Why does the RDP allow shorter surface intervals than the US Navy tables?

The RDP uses a 60-minute gas washout tissue for surface interval credit calculations, while the original US Navy tables used a 120-minute tissue. Because the RDP assumes nitrogen clears faster during the surface interval, it calculates less residual nitrogen remaining — which produces shorter required surface intervals and longer adjusted no-decompression limits on repetitive dives.

RDP and Decompression Theory — PADI Divemaster and Instructor Exam Study Notes

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The RDP section of the PADI Instructor Exam covers three areas: the theory behind how dive tables work, how to use the eRDPml in all four operating modes, and how to use the printed RDP Table correctly. Start with Decompression Theory if you want to understand why the rules exist — or go straight to the tool you need to practise.

Where to start If decompression theory is new to you, work through it first — the concepts underpin everything else. If you are already confident on theory and need to practise calculations, go directly to the eRDPml or RDP Table sections.

Section 1

Decompression Theory

Half-times, theoretical tissue compartments, M-values, surface interval credit, and why Navy tables and the RDP are not interchangeable. Seven pages.

Section 2

eRDPml

All four operating modes — Dive Planning, Maximum Depth, Surface Interval, and Multilevel — with step-by-step worked examples and practice questions. Five pages.

Section 3

RDP Table

How to use Tables 1, 2, and 3 for single and repetitive dives. ABT, RNT, and TBT explained with worked examples and a 10-question practice quiz.

Mixed Exam

Realistic IDC Practice Exam

12 questions matching the real PADI IDC written exam format — decompression theory, RDP rules, and eRDPml calculations all in one paper.

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