How Spaced Repetition Works
The science behind your review schedule
The Forgetting Curve
In the 1880s, psychologist Hermann Ebbinghaus discovered that memory decays exponentially after learning. Without review, you forget roughly 70% of new material within 24 hours.
This isn't a flaw - it's how the brain works. Your memory naturally filters out information it doesn't encounter again. The key insight: each time you successfully recall something, the forgetting curve flattens and the memory lasts longer.
How Spaced Repetition Fixes It
Spaced repetition is a study technique that schedules reviews at increasing intervals. Instead of cramming everything the night before an exam, you review each concept right before you would have forgotten it.
The first review might come after 1 day. If you get it right, the next review comes after 2-3 days, then a week, then two weeks, then a month. Each successful recall makes the memory stronger and pushes the next review further out. Concepts you struggle with stay in frequent rotation until they stick.
How It Works in Symmetria
Every time you answer a practice question, Symmetria records your score and updates your review schedule. The system uses a scoring algorithm based on how well you did:
The interval grows by your ease factor (starts at 2.5x). You see this card less and less often as it becomes well-learned.
The interval grows modestly (1.2x). You knew it, but the system keeps it in closer rotation until you nail it consistently.
The interval resets to 1 day and your ease factor decreases. You'll see this card again tomorrow.
Same as 1/3 - resets to 1 day with a larger ease factor penalty. The card comes back frequently until you learn it.
Your Review Schedule
Here's what a typical interval progression looks like for a card you keep getting right (starting ease factor of 2.5):
| Review # | Interval | Next review in |
|---|---|---|
| 1st | 1 day | Tomorrow |
| 2nd | 2.5 days | ~3 days |
| 3rd | 6.6 days | ~1 week |
| 4th | 17.6 days | ~2.5 weeks |
| 5th | 47.5 days | ~7 weeks |
| 6th | 131 days | ~4 months |
| 7th+ | 180 days (cap) | ~6 months |
Any wrong answer resets the interval back to 1 day, so you re-learn it before moving on.
Tips for Effective Use
- 1.Study daily, even briefly. Ten minutes every day beats two hours once a week. Consistent short sessions keep your review queue manageable.
- 2.Don't skip due cards. When the system says cards are due, it means you're about to forget them. Reviewing on time is what makes the intervals grow.
- 3.Trust the system. It might feel odd to see a concept you “already know.” That's by design. The review is reinforcing your memory right before it would have faded.
- 4.Use Mixed Review. Interleaving topics (nomenclature, then polarity, then stereochemistry) strengthens recall more than practicing one topic in isolation.
How Exams Fit In
Practice exam answers also feed into the spaced repetition system. Each exam question is scored as right or wrong (1/1 or 0/1), and the result updates the same review schedule as regular practice. So taking a practice exam doesn't just test you - it also trains your long-term memory.