These are the rules:
1. The numbers you can use are from 1 to 9.
2. In each row and in each column each number can appear only once just like in a normal Sudoku.
3. In a region (an area of 3x3 fields see the bold lines) each number can only appears once.
4. The numbers that are printed around the sudoku puzzle in the bold lines are the sum of the first 3 fields next to the sum. The sums in the corners are the sum of the 3 diagonal fields in the region.
To create your printable Sum Sudoku puzzle is extremely easy. Select how many fields in the puzzle should be printed with the number. And then you click on download the Sum Sudoku puzzle. It will create a pdf file for you. This pdf file contains 2 pages, one page is the puzzle and the second page contains the answer sheet.
Every Sum Sudoku puzzle is dynamically created. Therefor every puzzle is unique and you can download as many puzzle as you need.