Denys Fisher sale in Schofields department store in Leeds in 1965. A year later, Fisher licensed Spirograph to Kenner Products in the United States. In 1967 Spirograph was chosen as the UK Toy of the Year. Denys Fisher Toys, which also produced other toys and board games, was sold to Palitoy in 1970 and it was subsequently bought by Hasbro. Through the 1980s & 1990s Fisher continued to work with Hasbro in developing new toys and refining Spirograph. Denys Fisher Toys produced the following toys and games: Denys Fisher Denys Fisher (11 May 1918 – 17 September 2002) was an English engineer
Geometric calculus the correspondences of the differential form its derivative and its Hodge dual embed the theory of differential forms within geometric calculus. Following is a diagram summarizing the history of geometric calculus. Geometric calculus In mathematics, geometric calculus extends the geometric algebra to include differentiation and integration. The formalism is powerful and can be shown to encompass other mathematical theories including differential geometry and differential forms. With a geometric algebra given, let "a" and "b" be vectors and let "F(a)" be a multivector-valued function. The directional derivative of "F(a)" along "b" is defined as provided that the limit exists, where the