JonnnnY: Once again, very nice job :) I started making these puzzles for myself because I couldn't find a user interface that i liked, so i customized my own game. I'm glad you seem to like them as much as I do! Any more suggestions would be welcome.
Corgh: I don't think it is programmed wrong, more likely you are doing something wrong... Though I am pretty sure all the puzzles have only one solution, it is programmed so that as long as your answers all add up correctly, you win.
keyboard control: wasd or arrow keys.
boxes having the option for multiple entries was an intentional feature to allow all possibilities to be entered and then narrowed down. if a box has "12" in it and you hit "1" again it will erase the 1 and leave the 2.
thanks for the input everyone!
click the "check" button. if your math is good, you will get a green checkmark next to it on the "puzzles" screen. as far as i know there is only one solution per puzzle, but as long as everything adds up ok, it will give you the green checkmark.