Divide the grid into nine non-overlapping regions each consisting of nine orthogonally connected cells. Place the digits 1-9 once in each row, column, and region. The grid is covered in fog. Placing a correct digit in a cell lifts fog in that cell and possibly other cells; revealing new clues. Some cells contain a grey square inside them. The digit in such a cell is equal to the sum of the (up to 8) surrounding digits that are in different regions. Digits separated by a white dot differ by 1 and belong to the same region. A digit N on an arrow counts how many cells it sees of its region in the indicated direction, including itself. Region borders block vision. Additionally, the digit N+1 must appear immediately behind the first seen region border. Each arrow MUST therefore see a region border within the grid.