In SM-2, how does the ease factor update after a review?

After each pass, EF is adjusted from your grade $q$ — good grades raise it, mediocre grades lower it — with a hard floor of 1.3.

$$EF' = EF + \big(0.1 - (5-q)\times(0.08 + (5-q)\times 0.02)\big)$$

Worked cases:

• $q = 5$ (perfect): $EF' = EF + 0.1$ — the card gets easier, interval grows faster.
• $q = 4$: $EF' = EF - 0.0$ (roughly unchanged).
• $q = 3$ (correct but hard): $EF' = EF - 0.14$ — the card gets harder.

EF starts at 2.5 and can never drop below 1.3, which caps how tightly a stubborn card can be scheduled.