Steve Rowley writes: << I was explicit about saying I used only computer time, and that Dan's suggested metric didn't seem to mean much in terms of computer time.

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It's hard to be sure, of course, but the computer programs that solve Sudoku puzzles have algorithms that I suspect aren't all that different from what humans use to solve by hand. So my guess is that Steve's result (and thanks for taking the time to test it!) is indicative that my suggested metric is a dud. And it seemed so promising at first! Oh, well. --Dan