The Leitner system

Picture five boxes. A new card starts in the first one. Every time you get it right, it moves up a box and comes back later. Every time you miss it, it falls back to the first box and returns tomorrow.

What you know well spaces itself out. What resists comes back often. You decide nothing: you answer, and the schedule settles itself.

1. Box 1 back tomorrow
2. Box 2 back in 3 days
3. Box 3 back in 7 days
4. Box 4 back in 14 days
5. Box 5 back in 30 days

The method was described in 1972 by Sebastian Leitner, a German science journalist. It predates computers by decades — it works with cardboard index cards.