Spaced Repetition is a tried and tested revision technique which is commonly used with flash cards, and helps to focus on weaknesses and avoid wasting time on items already well known. Chinese Drill automates this process.

If you answer a new question incorrectly in a Lesson, it is scheduled for your next Revision session (although it will only appear if the level and lesson is set to include the lesson). If you answer it correctly, it is scheduled for the next Revision session after that.

Each time you answer a question correctly in a Revision session, the length of time until it is asked again is doubled. So for example, if you take a Lesson on Day 1, get a particular question right, and do a Revision session each day after that, you will be asked the same question on Day 3, Day 7, Day 15 and so on as long as you answer it correctly each time. If you answer incorrectly, you are asked again in the next session, and the sequence will start again – see the diagram below.

A maximum revision interval is set in the app Settings. Even if a question is answered correctly each time, it will be asked again at the latest when this interval is reached. The user can change or remove this maximum altogether.