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Spirograph is a trademark of Hasbro, Inc., for a geometric drawing toy, which produces mathematical curves of the variety technically known as hypotrochoids. The word has also been applied to a variety of software applications that display similar curves.
The Spirograph was invented by Denys Fisher, who exhibited it in 1965 at the Nuremberg International Toy Fair. Distribution rights were acquired by by Kenner, Inc., who introduced it to the United States market in 1966.
A Spirograph consists of a set of plastic gears and toothed rings. The gears fit inside the rings (but not precisely), in such a fashion that they rotate around the inside. To use it, a sheet of paper is placed on a heavy cardboard backing, and one of the plastic pieces is pinned to the paper and cardboard. Another plastic piece is placed so that its teeth engage with those of the pinned piece. For example, a ring may be pinned to the paper and a small gear placed inside the ring (although other arrangements are possible). The point of a pen is placed in a hole in the moving piece, so that it can draw a curved line on the paper as the hole moves. The pen is used both to draw and provide motive force; some practice is required before the toy can be operated without disengaging the fixed and moving pieces.
The term "spirograph" has also been applied to the class of curves that can be produced with the toy, so in this sense it may be regarded as a synonym of hypotrochoid. Also, a particular planetary nebula that displays delicate, poorly-understood, spirograph-like filigree has been nicknamed the Spirograph nebula.
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