The method
Why waiting makes you remember.
Pulse is one study loop, but underneath it is a century of quiet research on forgetting. Here is the short version — enough to make your own study choices deliberate.
Quiet notes while you study
Small optional asides explaining what the schedule just did. Off by default.
The forgetting curve
In the 1880s Hermann Ebbinghaus memorised nonsense syllables and measured how fast he lost them. Recall drops steeply within hours, then flattens. Each successful review makes the curve shallower, so the same material survives longer before the next look.
Retrieval, not rereading
Pulling an answer out of memory strengthens it far more than reading it again. That is why Pulse hides the answer until you commit: the effortful attempt is the study, and the reveal is only the check. Rereading feels fluent and teaches less — a well-documented illusion.
Desirable difficulty
Robert Bjork's phrase for the useful kind of struggle. A review that arrives just before you would have forgotten costs the most effort and buys the most durability. Too early is wasted; too late is relearning from scratch. Every spacing system is an attempt to aim at that moment.
Spacing beats cramming
The same total minutes spread across days produce substantially better long-term retention than one block. Cramming wins tomorrow's exam and loses the month.
Ways people space
The Leitner box1972
Physical cards in numbered boxes. Right answer moves a card one box out and it gets reviewed less often; a wrong answer sends it back to box one. Simple, tangible, and the ancestor of everything below.
Graduated interval recall (Pimsleur)1967
A fixed ladder of intervals — seconds, then minutes, then days — applied to everyone identically. Predictable and easy to follow, but blind to whether this particular item is hard for you.
SM-2 and the SuperMemo family1987
Piotr Woźniak's algorithm gives each card an ease factor that grows or shrinks with your ratings, multiplying the interval each time. This is the engine behind Anki's classic scheduler. Powerful, and famously fussy when a backlog builds up.
FSRS2022
A modern model that tracks three quantities per card — difficulty, stability, retrievability — and fits them to your own review history, scheduling for a retention target you pick. More accurate, less hand-tuned, and now Anki's default.
Free recall and interleaving—
Not scheduling at all: writing down everything you remember from a topic, and mixing related subjects rather than blocking them. Both pair well with card review and cover what isolated cards miss.
What Pulse does
Pulse uses a deliberately small Leitner-style ladder rather than a fitted model. Three ratings, one growing sequence of rest periods, no hidden parameters to tune.
- Knew moves the card one rung up the ladder: 1, 3, 7, 16, 35 days. After the last rung it stays there.
- Shaky halves the rest period and brings the card back later in the same round.
- Missed resets the ladder to zero and returns the card very soon.
- A card you needed a hint for is scheduled as shaky even if you rated it Knew — the unaided attempt hasn't happened yet.
- After three tries in one round a card is set aside, still due. Grinding one card is a poor use of a session.
- A round is capped at thirty due cards, weakest first, so a large deck stays finite.
Honest caveat: this ladder is coarser than SM-2 or FSRS. It trades precision for something you can hold in your head — you always know why a card came back.