Pattern Description from Knitting Rules!: “This method is a bit of a cheat, which should be an indication that I thought it up myself and it might not have much to do with pi. I offer it here because it has no math - none, and I thought you might find this a relief. I was thinking about when you decrease for the top of a hat, and if you decrease at the right rate and slope, the top of the hat is a perfect flat circle with a definite pillbox feel. I monkeyed around a little, not with a calculator but with some needles and yarn, and discovered that this works.”

This pattern may be found on pages 178-180 of Knitting Rules!