Leitner system

In the Leitner system, correctly answered cards are advanced to the next, less frequent box, while incorrectly answered cards will return to the first box.
An alternative method where incorrect answers are only moved back by one box

The Leitner system is a widely used method of efficiently using flashcards that was proposed by the German science journalist Sebastian Leitner in 1972. It is a simple implementation of the principle of spaced repetition, where cards are reviewed at increasing intervals.