Scheduling Reviews With SM-2

spaced repetition

Part of: AI Flashcard Generator

A flashcard app that shows every card every day wastes the learner's time on cards they already know. Spaced repetition shows a card right before you would forget it. Easy cards come back after weeks, and hard cards come back tomorrow. This lesson adds the scheduler that decides when each card is due. The SM-2 algorithm. SM-2 was published in 1987 for the SuperMemo software, and Anki still uses a close relative of it. Each card carries three numbers. - reps is how many times in a row the learner has recalled it correctly. - interval is how many days until the next review. - ease is a multiplier for how fast the interval grows. It starts at 2.5. After each review the learner grades their recall from 0 to 5, where 5 is instant and 0 is a blank stare. Grades below 3 count as a miss. The update rule. A miss sends the card back to the start with a one-day interval. A hit grows the interval, first to 1 day, then 6, then by multiplying with the current ease. The ease then shifts with the grade. A 5 nudges it up by 0.1, a 4 leaves it unchanged, and a 3 drops it by 0.14. It never goes below 1.3, or a card graded 3 over and over would end up with an interval that barely grows. Where the stat

Challenge: Replay a Card's History