Normal sudoku rules apply. 9 cells in the grid are “doublers”, one in every row, column, and 3x3 box, each containing a different digit. The value of a doubler cell is double the digit in that cell. Values on an arrow spell the coordinates for the value that is their sum. The row value is on the start of the arrow and the column value on the tip. Eg if an arrow contained the values 15, then a 6 (or a doubled 3) is placed in R1C5. Each arrow indicates a different cell.