Learning Science

What Is Spaced Repetition?

The science-backed study technique that helps you remember anything long-term by reviewing at the right time.

The Forgetting Curve Problem

In 1885, German psychologist Hermann Ebbinghaus discovered that we forget approximately 70% of new information within 24 hours unless we actively review it. This phenomenon is known as the forgetting curve.

Traditional studying — re-reading notes, highlighting, cramming before exams — doesn't work because it doesn't interrupt the forgetting curve at the right moments.

Memory Retention Over Time

Day 1
Day 2
Day 4
Week 1
Month

Without review, memory drops rapidly — the forgetting curve

How Spaced Repetition Solves This

Spaced repetition interrupts the forgetting curve by scheduling reviews at increasing intervals. Each time you successfully recall something, the next review is pushed further into the future.

For example: you learn a fact today, review it tomorrow, then in 3 days, then 7 days, then 2 weeks, then a month. Each review strengthens the memory and extends how long you retain it.

Review 1
After 1 day
Review 2
After 3 days
Review 3
After 7 days
Review 4
After 21 days

The SM-2 Algorithm

Etch utilizes the SM-2 spaced repetition algorithm developed by Dr. Piotr Woźniak of SuperMemo World. For more information on the original research and newer proprietary iterations, visit SuperMemo World.

After each review, you rate your recall:

Again
Didn't remember
Hard
Struggled
Good
Remembered
Easy
Effortless

The algorithm adjusts each card's interval based on your rating. Cards you find easy are shown less often. Cards you struggle with appear more frequently until they're mastered.

Why Spaced Repetition Works

Active Recall

Testing yourself is far more effective than passive reading. Flashcards force active retrieval.

Optimal Timing

Review right before you forget. This sweet spot maximizes memory strengthening per session.

Measurable Progress

Track your retention rate and see concrete improvement over days and weeks.

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