1.) Crosses added automatically (permanent) should be a different color than ones added manually.
2.) There should be an additional indication when you have too many squares filled around a number, rather than just missing the dot so you know it's "wrong".
3.) A button to clear the current puzzle, rather than having to quit and restart? Or at least an undo button.
4.) Crosses should automatically be added over other color numbers when you're working on another, since you can never color over them.
5.) Autofill in 9s, just like crossed-out zeros
6.) The first zoom level should try and fit the puzzle to the screen (eg, I shouldn't have to manually max the zoom in every time I start a 5x5 or a 10x10 puzzle)
Otherwise, a great game!
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