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The originator of this book-test method is Jim Sherman. It was marketed by the National Magic Co. in 1938 (this information discovered by Max Maven). The original used two metal cards with a rectangular window cut into them; one gimmicked, the other for examination. The application of the Wordo principle to a gimmicked paper clip is Bruce Elliott's, and appears in “Fate”, his trick in Phoenix, No. 177, May 6, 1949, p. 708.