A Killer Sudoku is the same as a Calcudoku puzzle, except:
the operator is always + (and not shown)
every 3×3 box has the numbers 1..9 exactly once
a cage also can not have duplicate numbers (!)
You can solve the puzzle using the number + arrow keys, or the mouse. Use shift + number to toggle guesses, the space bar to clear a cell, and 'backspace' for undo. Press '=' to highlight the number in a cell.