Tenth Box
Rule
The nine centre cells of each 3x3 box (highlighted) form a "Tenth Box", which must also contain the digits 1-9 without repetition. Each regular 3x3 box has all its clues projected on to the Tenth Box. Separate line segments remain as separate clues in the tenth box. In other words, the Tenth Box contains a copy of every clue in the puzzle.
Building the Tenth Box
To create the Tenth Box, take the centre cell from each of the nine standard 3×3 boxes and place them into a new 3×3 box in the same relative position. The animation shows how each highlighted cell is copied into the Tenth Box.
How Clues Transfer
Each standard 3×3 box projects its clues onto the Tenth Box. A clue is copied into the corresponding cells of the Tenth Box using the same relative positions. Separate clues remain separate, even if they overlap after projection.
