Logarithms from a cheap necklace

“Leibniz’s recipe for determining logarithms in this way is delightfully simple and can easily be carried out in practice using, for example, a cheap necklace pinned to a cardboard box with sewing needles.”

So wrote Viktor Blåsjö, in the essay “How to Find the Logarithm of Any Number Using Nothing But a Piece of String,” in the College Mathematics Journal, in 2016.