Normal sudoku rules apply. If a cell with an arrow contains the digit N, then the straight line starting in that cell and extending N cells in the arrow’s direction (including the arrow cell) is a valid region sum line: it must cross at least one 3×3 box border, and box borders divide it into segments with equal digit sums. E.g. if r1c1 = 5, then r1c1+r1c2+r1c3 = r1c4+r1c5.