Normal sudoku rules apply. Digits in a cage must sum to the small clue in the top left corner of the cage. Digits may not repeat within a cage. Every digit, except the digit in the centre (r5c5), has a 'partner digit' that is always placed in the cell 180° rotationally symmetrical to its own, rotated around the centre of the grid. Which digits are paired up must be deduced by the solver. (eg If the digits 1 and 2 turned out to be a rotational pair and r2c4 is a 1, r8c6 must be a 2.)