The Leitner System was designed by German scientist, Sebastian Leitner, and involves studying with flash cards and five boxes. All your flash cards start in Box 1. When you revise a card, if you get it right, the card moves to the next box (Box 2). If you get it wrong, it goes in Box 1. The next day you study the cards in Box 2 (the ones you answered incorrectly the day before). If you get it right, it moves to the next box (Box 3) but if you get it wrong it goes back in Box 1. 
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You revise the boxes on the following days:

• Box 1 — Every day
• Box 2 — Every 2 days
• Box 3 — Every 4 days
• Box 4 — Every 9 days
• Box 5 — Every 14 days.