Select the game difficulty. Harder games have more balls and bigger black box than easier games. You can also play with a custom difficulty level that you can set up in the setting dialog of KBlackBox.

Note: games with 4 balls or less can always be solved with certainty! That is not the case for games with 5 balls or more.

In this dialog, you can customize the number of balls, columns and rows of the black box in the custom difficulty level.