Why you forget dive theory (and how to make it stick)

On the last day of your course, you could explain why your tank empties faster at depth, what to do when your buddy disappears and how long to wait before flying home. Six months later, someone on a dive boat asks, and the answer is fuzzy. Everyone’s memory behaves this way, and the pattern was first measured more than 140 years ago.

What is the forgetting curve?

The forgetting curve shows how fast you lose what you learned when you don’t use it: steeply at first, then more and more slowly. The German psychologist Hermann Ebbinghaus measured it on himself in 1879 and 1880 and published it in 1885. He memorized lists of nonsense syllables, then measured how much effort it took to relearn them after different delays. Whatever effort he saved compared with the first time showed what he still remembered.

In 2015, Jaap Murre and Joeri Dros repeated the experiment, with Dros as the only subject: about 70 hours of learning and relearning lists. Their curve was very similar to Ebbinghaus’s, apart from a lower value at 31 days.

Dive theory makes more sense than nonsense syllables, so your own numbers will differ. The shape carries over: the biggest loss comes early, and a memory you never use keeps fading through the months between your course and your next dive trip.

Why does rereading feel like it works?

Rereading feels like it works because the material gets familiar, and familiar feels like known. A classic experiment shows the gap. In 2006, Henry Roediger and Jeffrey Karpicke had students learn short passages, one about the sun and one about sea otters. Some read a passage four times. Others read it once, then wrote down everything they could remember, three times, with no feedback.

Five minutes later, the readers won: they recalled 83% of the ideas, against 71%. One week later, the result flipped. The students who had tested themselves recalled 61%, the readers 40%. And the readers felt more confident they would remember.

Divers fall into the same trap: a manual you’ve reread feels known until someone asks you, with no notes, what you’ll do if you lose your buddy.

What is spaced repetition, and why does it work?

Spaced repetition means coming back to the same material in several sessions separated by time, instead of cramming it into one long block. The evidence that it works is broad. A 2006 review by Nicholas Cepeda and colleagues pooled 839 assessments from 317 experiments in 184 articles: spaced study beat massed study, and the best gap between sessions grew with how long you need to remember. A 2008 study by the same group tested more than 1,350 people. For a test a week away, the best gap was about 20 to 40% of that week, roughly 1.5 to 3 days. For a test a year away, it was about 5 to 10% of the year, roughly 2.5 to 5 weeks.

In 2013, John Dunlosky and four colleagues rated ten common study techniques. Only two earned their top rating:

How do you make dive theory stick?

You make dive theory stick by turning it into questions and answering them a little at a time, over weeks.

1. Test first, read second. Try the question, then read the explanation. The effort of recalling is what strengthens the memory.
2. Space your reviews. For an exam a week away, review every two or three days. To keep it for a season, come back every few weeks.
3. Mix topics. Pressure, hand signals and flying after diving in one short session beats an hour on pressure alone.
4. Explain the wrong answers. Our list of Open Water questions divers get wrong shows how.
5. Put safety first. Out of air, lost buddy, a diver with symptoms after a dive: these are answers you’ll need in seconds, with no notes.
6. Go back before a trip or a new course. Advanced, Rescue and Divemaster all build on your Open Water theory. Our study plans for the Open Water exam and the divemaster theory exam put this into a calendar.

Try a safety question now, then try it again next week without looking:

Try a question from the app

safety stop

What is the recommended safety stop?

1. A1 minute at 3 m (10 ft)
2. B3 minutes at 9 m (30 ft)
3. C5 minutes at 9 m (30 ft)
4. D3 minutes at 5 m (15 ft)

Show the answer

Answer D. 3 minutes at 5 m (15 ft), on every dive unless an emergency prevents it. It adds a margin against decompression sickness.

How does Octo’s spaced review work?

Octo schedules your reviews for you, based on the questions you miss. Each of its 62 short lessons, from Open Water to Divemaster, ends with six questions, each with the right answer and an explanation. A question you miss comes back the same day, then at longer and longer intervals. Safety questions come back more often. A daily goal, a day streak, badges and a Home Screen widget help you keep the habit, and each level has a 30-question practice exam to show where you stand. The details are on how Octo works, and you can try one question per lesson on the practice pages.

Frequently asked questions

Why do I forget what I learned in my scuba course?

Because memories you don’t use fade, fastest in the first hours and days. Ebbinghaus measured this forgetting curve in the 1880s and a 2015 replication found a very similar shape. A course packs a lot of theory into a short time, and if you don’t use it again until your next trip, much of it needs relearning. Short, spaced self-tests slow the loss.

What is the best way to study dive theory?

Test yourself and spread your sessions out. A 2013 review of ten study techniques by Dunlosky and colleagues gave its top rating to only two: practice testing and distributed practice. In practice, answer questions from memory, check the explanation, and come back to the ones you missed a few days later rather than rereading the manual.

How often should you review dive theory?

It depends on how long you need to remember it. In a 2008 study by Cepeda and colleagues, the best gap between reviews was about 20 to 40% of the time until a test a week away, and about 5 to 10% for a test a year away. For an exam next week, that’s every two or three days; for a whole season, every few weeks.

Is rereading the dive manual a good way to study?

Not on its own. Rereading makes the text familiar, which feels like learning, but in Roediger and Karpicke’s 2006 experiment, students who tested themselves remembered far more a week later than students who reread: 61% against 40%. Read the manual once to understand, then switch to answering questions and checking the explanations.

What is the testing effect?

The testing effect is the finding that retrieving information, by answering a question or recalling it without looking, strengthens memory more than studying it again. Roediger and Karpicke showed it with prose passages in 2006: repeated testing beat repeated reading on tests two days and one week later, even though rereading won on a test five minutes later.

Sources

1. Hermann Ebbinghaus, Memory: A Contribution to Experimental Psychology (1885; English translation 1913), Chapter 7, Classics in the History of Psychology
2. Murre and Dros, Replication and Analysis of Ebbinghaus’ Forgetting Curve, PLOS ONE 10(7), 2015
3. Roediger and Karpicke, Test-Enhanced Learning, Psychological Science 17(3), 2006
4. Cepeda et al., Distributed Practice in Verbal Recall Tasks, Psychological Bulletin 132(3), 2006
5. Cepeda et al., Spacing Effects in Learning, Psychological Science 19(11), 2008
6. Dunlosky et al., Improving Students’ Learning With Effective Learning Techniques, Psychological Science in the Public Interest 14(1), 2013