Normal sudoku rules apply. The grid is partly covered in fog. Placing correct digits may clear fog revealing other clues. No guessing is required. A digit in a square indicates the total number of digits smaller than itself that it 'sees' in all the four cardinal directions (North, East, South, West) along its row and column. In each direction, it 'sees' ALL digits smaller than itself until vision is blocked by a digit greater than itself or the edge of the grid. (For clarity it does not see itself). If a black dot separates two digits, one of those digits is double the other.