Assign numbers 1 to 9 in the empty boxes so that in each 3x3 block, row and column all numbers from 1 to 9 are present without repetitions. The dotted lines indicate areas which also contain a non-repeating set of digits. These squares can be added together to produce the sums shown in the clues.
Click on the numbers in the top right part of the screen to select the number. Click on an empty box to write the number. Click on a previous written number to delete it.
Game is completely controlled by mouse.
Medium #2 is easily the hardest puzzle in here. On the Hard puzzles I at least had something to go on as a starting point; Medium 2 provides nothing of the sort.
Overall, it needs pencilmarks in the corners, and it would be nice to be able to enter a number by mousing over it and pressing the desired number. The music's nice though.