Systems Study Guide v0.8.5

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🧠 Free Spaced Repetition Scheduler (FSRS)

FSRS is the modern spaced-repetition algorithm this app uses to decide when to show you each question. Instead of fixed intervals, it models how your memory of every card fades over time and schedules each review for the moment you’re about to forget — so you spend less time reviewing and remember more.

After every answer, your result and confidence update that model: a wrong answer resets the card, while a correct one pushes its next review further out based on how well you knew it. The details below explain exactly how.

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Your Answer → FSRS Rating

Two things are combined each time you answer: whether you got it right or wrong, and your confidence. Together they produce one of four FSRS ratings.

ResultConfidenceFSRS RatingEffect
❌ WrongAnyAgainCard resets immediately
✅ CorrectGuessedHardShort interval increase
✅ CorrectUnsureGoodNormal interval increase
✅ CorrectKnew ItEasyLarge interval increase (+87%)

⚠️ Being wrong always produces Again, regardless of confidence. You cannot extend an interval with a lucky guess.

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Two Numbers Drive Everything

Each card stores exactly two values that control all scheduling. These are saved in your progress file after every answer.

Stability (S)
How many days until your recall probability drops to 90%. A new "Knew It" card starts at ~8 days. A well-established card might have S = 200+ days.
Range: 0.001 → unlimited days
Difficulty (D)
How inherently hard this card is for you. Shaped by your first answer and drifts slowly over time. A low score means you find it easy; a high score means you keep struggling with it.
Range: 1.0 (easy) → 10.0 (hard)
📉

The Forgetting Curve

Retrievability (R) is the algorithm's live estimate of your recall probability right now. It decays every day you don't review a card.

R(t) = (1 + FACTOR × t / S) DECAY
  • t = days since last review
  • S = stability (higher = slower decay)
  • FACTOR ≈ 19.97  |  DECAY = −0.1542 (fixed constants)

This app schedules your next review for the day R(t) would hit 90% — the desired_retention setting. A card with S = 10 days gets reviewed in ~10 days; S = 100 days gets reviewed in ~100 days.

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How Stability Grows (or Shrinks)

After each review, stability is recalculated. The exact amount depends on your rating, current difficulty, and how well you recalled it.

Easy Stability grows ~87% more than normal. Best long-term payoff.
Good Normal growth. The expected, healthy path.
Hard Growth is reduced by ~40%. Card is penalised for struggling.
Again Stability collapses. The more established the card was, the more you lose.

Reviewing a card later than scheduled (lower R) actually produces a bigger stability gain — FSRS rewards spacing things out.

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Card Lifecycle

Learning
Brand new card. Reviewed at 1 min → 10 min intervals to build initial stability. Good or Easy moves it to Review state.
→
Review
Established card on a long-term schedule (days to months). This is the normal state for cards you know well.
→ (wrong)
Relearning
Failed a Review card. Reviewed again in 10 minutes, then graduates back to Review with reduced stability.
⭐

The Mastery Threshold

A card is shown as Mastered on your Progress screen when all three conditions are met:

≥ 3 answers
You must have answered this card at least three times, in any study mode.
AND
Graduated
The card has passed its FSRS learning steps and its last answer was correct — a wrong answer sends it back to relearning.
AND
Not due
Its next scheduled review is still in the future.

Mastery is sticky — it never fades quietly with time. When a card's review date arrives it moves to Due; one correct review makes it mastered again with a longer interval, while a wrong answer demotes it immediately.

💡 Study Tips
  • Daily Habit: Consistency is key. Even a short 10-question session keeps your streak alive and clears your due queue.
  • Be Honest: Only select "Knew It" if you were absolutely certain. FSRS relies on your honest feedback to schedule effectively.
  • Trust the Algorithm: Don't cram! Focus on reviewing your "Due" cards every day.
⚡ Cram Mode

Enable ⚡ Cram Mode when you have a test coming up and need to cover all cards fast. It uses a Leitner box system — cards you get wrong drop back to Box 1, correct ones promote toward Box 3. The session always shows your weakest cards first.

  • Box 1 — Weak: Shown every session until you get them right.
  • Box 2 — Learning: Seen and correct at least once.
  • Box 3 — Ready: Consistently got right. Goal is all cards here.

Cram sessions still count toward your long-term FSRS progress.

Add to Your Home Screen

  • Works offline — study anywhere, no signal needed.
  • Opens full-screen — like a real app from your home screen.
  • Keeps your progress safe — a browser can clear saved data (on iPhone, after about a week unused); the installed app keeps it.

No account, no tracking. Your progress is saved only on this device and is never uploaded or sent anywhere.

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Spaced Repetition Forecast

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Total Reviews Left

Start a Session

?Leitner box system for test prep. Prioritises weak cards. Ignores FSRS scheduling. ?Randomises question order each session. ?Only shows questions you've answered incorrectly at least once. ?Only shows questions FSRS has scheduled for review today. ?Only shows questions you've flagged with the 🚩 button during a quiz. ?Wrong answers loop back into the deck until you get them right. Only the first attempt is scored.

Recent Activity

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Session Complete

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Progress Dashboard

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Total Questions
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Days Studied
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Reviews Left
0% Mastered
FSRS Progress
Mastered0
Due0
Unseen0
0% Box 3
⚡ Cram Progress
Box 10
Box 20
Box 30

Progress Over Time

By System

Local Data

All your progress, session history, and FSRS scheduling data are saved locally and privately on your device — never uploaded or sent anywhere.

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