The object is to fill all empty squares using numbers 1 to 9 so the sum of each horizontal block equals the clue on its left, and the sum of each vertical block equals the clue on its top. In addition, no number may be used in the same block more than once. There is only one unique solution for each puzzle.
Click mouse on the desired square to open dial pad and then click on the desired number. To remove a number, repeat the above using X at the bottom of the dial pad. Numbers can also be placed by pointing mouse on the desired square and then typing with the keyboard.