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It's easy enough to work out the mechanics, but it's the time factor that puzzles me. They're so intricate and so precise, and often cover quite a large area, so I really can't see how they're done with a plank of wood, a bit of string, and a protractor, in the dark and in such a short space of time - and if the area was illuminated, surely by now someone would have spotted at least one of them being created.
Having said that, I knew a roguish farmer who thought he'd make a few bob by creating a very simple crop circle and charging people to see it, but he did it over the course of a day or two in daylight - and it was very, very simple indeed - and not terribly precise. Nothing like these things. Incidentally, his little scheme hit the rocks when he called a TV station and his girlfriend took fright and put a stop to it!