Normal sudoku rules apply. Along lines, the region sums form a consecutive ordered sequence. For example, the sum of the digits along the blue line within box 3 must be consecutive with the sum of the digits along that line in box 2 – and the sum of the digits along that same line in box 6 must be consecutive with the sum from box 2. And these sums must be ordered from lowest to highest (so the box 2 sum would always be the middle of that sequence).