Normal sudoku rules apply within the 9x9 grid. Digits along a thermometer must increase from the bulb end. Each digit in the 9x9 grid represents a skyscraper with a height corresponding to its value. Clues outside the 9x9 grid indicate how many skyscrapers can be seen, in total, when looking along that row or column from that direction. Taller skyscrapers block smaller skyscrapers from view.