Illustration of Leksell Stereotactic System While at the service of his mentor, Herbert Olivecrona, Lars Leksell sensed the need to further develop the concepts originally described by Horsley and Clarke in 1908. In 1949, he designed the first instrument to be based on the arc-center principle. The stereotactic system has undergone many refinements over the years; the frame on display was manufactured around 1980. original reference: http://www.neurosurgery.org/cybermuseum/stereotactichall/92exhibit.html