Question to those who do Sudoku puzzles, particularily but not exclusively to experts

[Zavulon]

I know how lame this thread is, but every time I've needed an answer I've gotten it here, and I don't know who else to ask. Hope you don't mind.

Here's the deal: I ride the DC Metro to work every day (for locals: from Greenbelt to Farragut North), and every day I buy the Washington Post and grab a copy of the Express, the Post's commuter paper.

On the train, I do the Sudoku puzzles in both papers to pass the time. On Monday, I got the perfect example of something that has bothered me ever since Sudoku became popular over here. The Express had a puzzle of "medium" difficulty, and the Post had one labeled "easy." Both papers get their puzzles from the same source, Pappocom.

So why the hell is it that I solved the "medium" puzzle in less than half the time that it took me to do the "easy" one, and why is this the case with medium / easy more often than not?

Actually, let's assume the last question was rhetorical, and let's go with this instead: do any of you know exactly how the powers that be determine the difficulty of a Sudoku puzzle? Certainly, those labeled "hard" are more difficult than those labeled "medium" or "easy," but why the hell is "medium" so often easier than "easy?"

Again, I know this thread is lame, but I'm guessing that at least one of you has the answer to this. Thanks for your time.

- Z.

[petronius]

1. I was thinking about that today - the 'easy' puzzle in the LA Times today

(only 2 difficulty stars) nearly kicked my ass. I've always imagined there was a computer program somewhere that spits these things out and assigns a difficulty, but I have no idea.

However, I've noticed that there are some tactics that I use frequently and others tht I don't - an easy puzzle that requires the deductions that I'm not used to making will seem more difficult...