Each checkbox corresponds to a specific total number of active cells in the local neighborhood. The neighborhood consists of the cell itself plus its six direct neighbors (left, right, up, down, front, back).

For an empty cell, the top row defines when it should become active. For a live cell, the bottom row defines when it should stay active.

In each row, checkboxes are ordered from lowest to highest total activity. If the checkbox for the current activity level is checked, the cell will be ON in the next step; otherwise it will be OFF.