It is supposed to be based on the techniques needed to solve the puzzle. Harder puzzles use more advanced techniques.
clickity click click done so easy ng
Done no greens
Wow, finished today's with no greens - unusual for me :)
Quick one - no greens
Bah. There's nothing like smugly patting yourself on the back 'cause you just spotted a locked quintuplet... only to realize that what's left is an orphan in both its box and its column. Hooray for doing things the hard way! :)