Mastery

Mastery is a measure of how well you know your repertoire. To generate this, we look at the spaced repetition interval for each move: roughly, how long Chessbook thinks you can go before you need to see that move again.

Fresh moves contribute almost nothing. Moves with longer intervals contribute more, up to a 100 day interval, which counts as fully mastered. The scale is logarithmic, so the first few days of interval help a lot, but going from 70 to 100 days matters much less than going from 1 to 10.

We then average that over the moves in your repertoire.

Note that this is based on the interval of reviews, not the time until your reviews are due. So mastery won't automatically go down if you stop reviewing for a couple months, even though lots of moves may become due. True mastery would be a score of 100% here and no moves due.