Normal sudoku rules apply. Digits on a blue line must have an equal sum within each 3x3 box that line passes through, regardless of how many times the line exits and re-enters a region. The area outside the grid is considered one region for purposes of this rule. Different lines may have different sums. Numbers outside the grid give the sum of the first N digits in their respective row or column, where N is the digit nearest the clue (inside the grid). Eg The following statements describe how these lines must be interpreted (rows/columns 0 and 10 indicate cells outside the 9x9 grid): Box 1: r0c1 + r1c0 = r1c2 + r1c3 + r2c1 + r3c1 + r3c2 & Box 7: r8c0 + r10c3 = r7c1 + r8c1 + r9c1 + r9c2\n