PADI Knowledge Reviews: Your Guide to Understanding Each Section

PADI Knowledge Reviews explained. Learn what each of the five Open Water knowledge reviews covers, how to study effectively, and where to find free practice quizzes to test your understanding.

PADI Knowledge Reviews: Your Guide to Understanding Each Section

Every diver remembers their first encounter with a PADI Knowledge Review. You finish a section of the eLearning, feeling like you absorbed the material, and then the questions pop up. Some feel straightforward. Others make you wonder if you read the same chapter.

Knowledge Reviews are the short quizzes at the end of each of the five eLearning sections in the PADI Open Water Diver course. They are open-book — PADI wants you to use your manual or eLearning to find the answers. This is not cheating; it is part of the learning process. By looking up the correct answers, you reinforce the material before the final exam.

This guide walks through each of the five Knowledge Reviews, explains what they cover, highlights the topics that trip students up most often, and points you to resources that help you prepare.

If you are still deciding whether to start the Open Water course, read our complete Open Water Diver certification guide first.

Knowledge Review 1: The Aquatic World (Physics & Physiology)

Purpose: Build your understanding of the underwater environment and how pressure affects your body.

Key topics covered:

• Boyle's Law — the relationship between pressure and volume (why equalization matters)
• Dalton's Law — partial pressures of gases (the basis for nitrox diving)
• Henry's Law — how gas dissolves in body tissues (the foundation of no-stop limits and decompression theory)
• Buoyancy basics — positive, negative, and neutral buoyancy
• How pressure affects vision, hearing, and breathing at depth
• Heat loss in water

Common trouble spots

Mixing up the gas laws. Boyle's Law deals with volume changes in a flexible container (your lungs, your ears). Dalton's Law is about the pressure contribution of each gas in a mixture. Henry's Law explains how gas comes out of solution — the core of decompression sickness. A good trick: Boyle = Breathing (lung volume), Dalton = partial pressure of each gas, Henry = How gas enters your tissues.

Pressure calculations. Make sure you understand that pressure doubles at 10 meters (2 atmospheres absolute) and triples at 20 meters (3 ATA). Many exam questions test this basic relationship.

Knowledge Review 2: Dive Equipment

Purpose: Learn the function, maintenance, and safe use of scuba equipment.

Key topics covered:

• Tank construction (steel vs. aluminum), sizes, and working pressure
• Valve types (K-valve vs. J-valve with reserve)
• Regulator stages (first stage, second stage, alternate second stage, SPG)
• BCD types and inflation systems (power inflator, oral inflator, dump valves)
• Wetsuit thickness and thermal protection
• Weight systems (integrated vs. belt) and proper weighting
• Equipment inspection and maintenance

Common trouble spots

Regulator stages. Students often confuse what happens at each stage. The first stage reduces tank pressure to intermediate pressure (~140 psi / 9.9 bar above ambient). The second stage further reduces it to ambient pressure on your inhale. The SPG reads tank pressure directly from the first stage high-pressure port.

Equipment malfunction procedures. Know what to do if your regulator free-flows, if your BCD inflator sticks, or if your weight belt releases accidentally. The final exam often presents scenarios rather than direct definitions.

Knowledge Review 3: Dive Planning and Procedures

Purpose: Learn how to plan safe dives, use dive tables or computers, and manage emergencies.

Key topics covered:

• No-stop limits (formerly called no-decompression limits)
• Nitrogen absorption and off-gassing
• Using the Recreational Dive Planner (RPD or wheel)
• Pressure groups, repetitive dives, and surface intervals
• Residual nitrogen time
• Dive computer operation and limitations
• Buddy system procedures
• Emergency procedures (out-of-air, entangled diver, unresponsive buddy)

Common trouble spots

Dive table calculations. This is the most calculation-heavy section. Practice determining your pressure group after a dive, finding the minimum surface interval, and calculating your new pressure group for a repetitive dive. If one step is off, every subsequent step will be wrong.

Residual nitrogen time vs. actual bottom time. Your computer tracks both, but the exam may ask you to calculate total bottom time including residual nitrogen on repetitive dives.

Emergency prioritization. Know the order of actions for common emergencies. For example: out-of-air — signal your buddy, establish air sharing, begin a controlled ascent. Do not skip steps.

Knowledge Review 4: The Dive Environment

Purpose: Understand the conditions you will encounter underwater and how to dive safely in different environments.

Key topics covered:

• Marine life identification and hazards (stinging creatures, biting creatures, poisonous vs. venomous)
• Environmental conditions (visibility, current, surge, waves, thermoclines)
• Tides and their effect on diving
• Boat diving procedures (entries, exits, anchor lines)
• Shore diving procedures
• Altitude diving considerations
• Environmental awareness and conservation

Common trouble spots

Hazardous marine life. You do not need to memorize every species, but understand the difference between venomous (injects toxin) and poisonous (toxic when eaten or touched), and know the general rules: look but do not touch, wear exposure protection, and maintain neutral buoyancy to avoid contact with the bottom.

Current diving. Know the difference between entering a current (swim against it at the start, ride it back) and drift diving (let the current carry you, the boat picks you up).

Knowledge Review 5: Recreational Dive Planning

Purpose: Bring everything together by planning actual dives using the tools and procedures learned in previous sections.

Key topics covered:

• Full dive planning from start to finish
• Calculating no-stop limits with repetitive dives
• Applying the Recreational Dive Planner across multi-day diving scenarios
• Minimum surface interval calculations
• Emergency assistance and accident management
• Dive logs and certification documentation

Common trouble spots

Multi-day dive planning. The most challenging questions involve planning three or four dives over consecutive days, including calculating pressure groups after each dive, determining required surface intervals, and ensuring every dive stays within no-stop limits.

Scenario-based questions. These questions do not test a single fact — they test your ability to apply multiple concepts together. Read the scenario carefully, note all the numbers (depths, times, surface intervals), and work through the problem step by step.

How to Ace Your Knowledge Reviews

1. Treat Them as Open-Book Learning

Knowledge Reviews are designed to be open-book. Do not try to answer from memory. Look up each answer in your manual or eLearning. The act of searching reinforces the material better than guessing.

2. Write Down Your Wrong Answers

Keep a running list of questions you got wrong or had to search hard for. Review this list before the final exam. Your weak areas are likely to appear again.

3. Use the RDP Wheel Actively

Section 3 and Section 5 include dive table questions. Practice with a physical RDP wheel if your instructor provides one, or use the digital version in your eLearning. Muscle memory with the tool helps you work faster and more accurately on the final exam.

4. Take Free Practice Quizzes

Once you finish all five Knowledge Reviews, take a comprehensive practice quiz to see how well the material has stuck. The questions are formatted similarly to the real exam.

👉 Take the Free PADI Open Water Diver Practice Quiz

This 20-question quiz covers topics from all five sections and gives you instant feedback on every answer. Use it to identify weak spots before exam day.

5. Review Related Articles

Some topics are easier to understand when you read about them from a different angle:

• What is No-Stop Time in Diving? — deep dive into no-stop limits and dive table theory
• What is DCI in Diving and What to Do About It — understand decompression sickness and prevent it
• Essential Safety Tips for Divers — reinforce emergency procedures
• Scuba Diving Equipment for Beginners — visual guide to the gear covered in Knowledge Review 2

Knowledge Reviews vs. Final Exam

The Knowledge Reviews are not just practice — they are the foundation. If you can confidently answer every Knowledge Review question without looking up the answer, you are ready for the final exam.

Frequently Asked Questions

Can I retake a Knowledge Review?

Yes. The eLearning system allows unlimited retakes. Each attempt shows different questions from the same topic pool.

Do Knowledge Review scores count toward my final grade?

No. Knowledge Reviews are completion-based — you must finish them, but your score does not affect your ability to progress. The final exam score is what matters for certification.

Are Knowledge Reviews the same for every PADI course?

Each PADI course (Open Water, Advanced Open Water, Rescue, Divemaster) has its own set of Knowledge Reviews. The format is the same, but the content is specific to that course level.

Are Knowledge Reviews available offline?

If you are using a physical PADI Open Water Diver manual, the Knowledge Reviews are printed at the end of each chapter. You write your answers directly in the manual and review them with your instructor.

How long should I spend on each Knowledge Review?

Most students spend 30–60 minutes per review, including looking up answers in the manual or eLearning. Take your time — rushing through them defeats their purpose.

Where can I find free practice for the final exam?

Take our free PADI Open Water Diver practice quiz to test your knowledge across all five sections before the real exam.