Normal sudoku rules apply. Digits on an arrow sum to the value in the diamond. If the arrow is horizontal, then the digit in the diamond indicates where the column number of the diamond appears in the row, e.g. if r9c5 is a 7 then r9c7 is a 5. Similarly, if the arrow is vertical, then the digit in the diamond indicates where the row number of the diamond appears in the column, e.g. if r2c7 is a 5 then r5c7 is a 2. If a diamond has arrows in both directions then it follows both rules.