Glossary:Difficulty

difficulty

estimation of element's difficulty in SuperMemo. Three main measures can be used to express difficulty:

1. current estimation of item's absolute difficulty estimated by Algorithm SM-17. This number ranges from 0 (for easy items) to 1 (for difficult items). It is displayed as Diff in the Element data window
2. current estimation of item's absolute difficulty estimated by Algorithm SM-15. This number ranges from 1.2 (for difficult items) to 6.9 (for easy items). It is represented by A-Factor and displayed as A-Factor in the Element data window
3. heuristic measure of difficulty based on the history of repetitions and displayed in the Element data window as Old (this measure can be used to sort collections that are to be used by other users; starting with easy items first)