.....I know what you mean and also I can look at a "so called completed puzzle" and not see why the screen didn't turn green......knowing that all the numbers are correct.......now scanning the puzzle to see which number(s) are out of place as my typing skills aren't that good or that I inadvertently switched 2 numbers when typing them in.......and when looking at an 8x8 my 72 year old eyes and brain just seem to "fog up" and for some time!!!(sometimes)