Each number to the right of the grid gives the sizes of the contiguous blocks of black squares within that row. Each number below the grid does the same for its column.
| To turn a square: | use this mouse button: | or this key with the mouse button: |
| black | left | none |
| white | right | Control |
| gray | middle | Shift |
You can drag the mouse to set a bunch of squares at one time.