the user to review the card again. Every time the user starts a review session, SuperMemo provides the user with the cards whose last review occurred at least I days ago. For each review, the user tries to recall the information and (after being shown the correct answer) specifies a grade q (from 0 to 5) indicating a self-evaluation the quality of their response, with each grade having the following meaning: 0: "Total blackout", complete failure to recall the information. 1: Incorrect response, but upon seeing the correct answer it felt familiar. 2: Incorrect response, but upon seeing the correct answer it seemed easy to remember. 3: Correct response, but required significant effort to recall. 4: Correct response, after some hesitation. 5: Correct response with perfect recall. The following algorithm is then applied to update the three variables associated with the card: algorithm SM-2 is input: user grade q repetition number n easiness factor EF interval I output: updated values of n, EF, and I if q ≥ 3 (correct response) then if n = 0 then I ← 1 else if n = 1 then I ← 6 else I ← round(I × EF) end if increment n else (incorrect response) n ← 0 I ← 1 end if EF ← EF + (0.1 − (5 − q) × (0.08 + (5 − q) × 0.02)) if EF < 1.3 then EF ← 1.3 end if return (n, EF, I) After all scheduled reviews are complete, SuperMemo asks the user to re-review any cards they marked with a grade less than 4 repeatedly until they give a grade ≥ 4. Non-SuperMemo implementations Some of the algorithms have been re-implemented in other, often free programs such as Anki, Mnemosyne, and Emacs Org-mode's Org-drill. See full list of flashcard software. The SM-2 algorithm has proven most popular in other applications, and is used (in modified form) in Anki and Mnemosyne, among others. Org-drill implements SM-5 by default, and optionally other algorithms such as SM-2 and a simplified SM-8. References External links Articles Tomasz P. Szynalski: Use spaced-repetition software (SRS) – An introduction to spaced-repetition and SuperMemo Pawel Kowalczyk: Learn English with SuperMemo – How SuperMemo can help learn English Patrick Kenny: Memory Software: SuperMemo – A guide to using SuperMemo to study Japanese Spaced repetition software