You don’t need to know any of this to use Memorics. It’s here for anyone who wants to know why a card comes back when it does.
The idea
You forget most of what you learn unless you come back to it, and you forget it in a fairly predictable way: quickly at first, then more slowly. Each time you manage to recall something, the memory gets stronger and fades more slowly than before. A recall that takes some effort, because you were close to forgetting, strengthens it the most.
So the best time to review a card is just before you’d forget it. Too early wastes your time on something you still know. Too late and you have to learn it again. Spaced repetition is about finding that moment for every card, so reviews get further and further apart: a day, then a few days, then weeks, then months.
The memory model
To find that moment, Memorics uses FSRS, an openly developed memory model that predicts how likely you are to remember a card at any point in time. For each card, it keeps track of two things:
- Stability: how many days it takes until your chance of remembering the card drops to 90%. A card you’ve just learned might have a stability of a day or two. One you’ve known for months might have a stability of a year.
- Difficulty: how hard the card is for you, from 1 to 10. The harder a card, the more slowly its stability grows with each review.
Both are worked out from your own answers on that card. The same card can be easy for you and hard for a classmate, and Memorics schedules it differently for each of you.
A card is due when your chance of remembering it has dropped to about 90%, so the time until a card comes back is its stability, rounded to whole days.
What your rating does
Each answer updates the card’s stability and difficulty, based on how long it’s been since you last saw it and how you rated it:
- Again: you forgot it. Its stability drops, it gets a little harder, and you learn it again right away.
- Hard: you remembered it, but only just. It comes back sooner than with Good, and gets a little harder.
- Good: you remembered it. Its stability grows, more so the longer it had been.
- Easy: you knew it right away. Its stability grows the most, and it gets a little easier.
The buttons always keep their order: Hard is never later than Good, and Easy is always at least a day later than Good. Each button shows when the card would come back, so you can see what your rating does before you press it.
Rating honestly matters more than rating kindly. Pressing Good on a card you didn’t really know pushes it further out, and you’ll likely have forgotten it by then.
Learning new cards
A new card isn’t scheduled after the first time you see it. In the session, it needs Good twice in a row (or Easy once), so it has been recalled once more after a short gap. Only then does it get its first interval of a day or more. Answers within the same day still count toward its memory, but they don’t grow it nearly as much as a review on a later day. A card you forget during a review goes through the same steps again. A card you review and remember is done with one Good.
A few more details
- Study days start at 4 in the morning, in your time zone. Studying at 1 a.m. still counts for the day before, and a card due “tomorrow” is due when your next study day starts.
- A little spread: from 3 days on, intervals are varied by a small amount, so cards you learned together don’t keep coming back together on the same day. The time on a button already includes it.
- Cards asked both ways are two memories: recalling “the dog” from “der Hund” isn’t the same as the other way round. Each way has its own stability and is scheduled on its own.
- Practice doesn’t count. Practice sessions never change a card’s schedule, so you can practice as much as you like without throwing off your reviews.
What a session asks, and in what order
A spaced repetition session first finishes the cards you started learning but didn’t finish. Then it asks the reviews that are due, the most overdue first, with the day’s new cards spread evenly among them, so you don’t face a pile of new cards at the end.
Within the session, cards are asked in rounds of up to 20. After each round, finished cards leave and waiting ones join. So a card you missed comes back within a few minutes, while what you just saw has faded enough that recalling it still takes effort. Within each round, Memorics shuffles the cards with a few rules:
- A card never comes twice in a row, and stays a few cards apart from where you last saw it.
- The two ways of a card stay apart, so one doesn’t give away the other.
- Similar cards are mixed: cards from the same subtopic, and cards of the same kind, don’t follow each other where it can be avoided. This is called interleaving. Switching between related material makes you work out each answer on its own, and helps you tell similar things apart, which is what an exam asks of you too.
How long it will take
Memorics times your answers, leaving out time spent reading a source and very long pauses, and works out your pace from your last answers. The time left in a session and on Today comes from that pace and from how many answers the cards still need. A new card needs a few answers, and a review usually one.
For exams, Memorics plans differently. See How exam plans work.