FSRS — Free Spaced Repetition Scheduler — is the algorithm underneath modern flashcard apps like Anki and ModernATC. It models three properties of every card you’ve seen (difficulty, stability, retrievability) and schedules each next review for the moment you’re about to forget it.
That last bit is the magic. Reviewing a card the day before you’d forget anyway is wasted effort; reviewing a week after you’ve already forgotten means you have to relearn from scratch. FSRS finds the sweet spot.
Why this matters for ATC studies
The .65 is dense and unforgiving. There are hundreds of defined terms, dozens of phraseology templates, and the test will pull from any of them. Trying to brute-force memorize the whole document with re-reading is a losing strategy: most of what you read on Monday is gone by Friday.
Spaced repetition turns the same time investment into long-term retention. The same hour spent on flashcards reviewed at FSRS intervals leaves you with much more recallable material than an hour of re-reading.
Why 90% retention
FSRS lets you set a target retention probability — the likelihood that you’ll recall a given card on its next review. The default is 90%. Lower (say 80%) means fewer reviews per day but you’ll forget more cards. Higher (say 95%) means more reviews per day for marginally better recall.
For ATC studies, 90% is the right starting point. The .65 is high-stakes — you can’t afford to be fuzzy on separation minima — but pushing to 95% adds noticeable daily review burden without commensurate test-day payoff.
Once you’re a few months in and your cards have stabilized, consider dropping to 85% on lower-stakes decks (definitions you don’t need word-perfect) and keeping 90% on phraseology and procedures.
How to rate yourself honestly
Most flashcard apps ask you to grade your recall after seeing the answer: Again, Hard, Good, Easy. The temptation is to be generous ("I almost got it") or harsh ("I want to see it again to be sure"). Both wreck the schedule.
The honest rule:
- Again if you couldn’t recall, even partially.
- Hard if you got it but with significant effort or hesitation.
- Good if you recalled it cleanly with normal effort.
- Easy only if it was instant and effortless, to the point you almost felt silly seeing it.
FSRS calibrates itself off these grades. Lying to it — in either direction — gives you worse intervals and ultimately worse retention.