I have been playing computer Sudoku games for two years. When I got my iPhone I need one because Sudoku is the best "waiting in line",etc., app to help me stay calm. I tried Sudoku Classic. It is great! Heres why: - simple to learn and use - I can play it one handed - I play it at the "Im good" level. This is about 35 givens. Solvable but not obvious. This means that some "notes" are required - the notes system is terrific! One extra touch and I am in notes. Then when I solve a square the notes are hidden. But if for some reason I need to erase the number for that square, the notes come right back! - I set it so that mistakes show instantly. They display in red. - any time I move away from the board, by going to another app or locking the display or by selecting Menu at the top, the clock stops - when I come back and have a game in progress, Continue is enabled on the menu. If I forget and try to start a new game, it warns me and lets me cancel. - on my iPad, I can set the display to 2x and it plays just like it was made for the iPad - from Help I can send an email to the developers I just love it.