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Until the late 19th century, slide rules had been constructed of boxwood and, occasionally, of brass or ivory. A great improvement was introduced in 1886 by Dennert and Pape in Germany by dividing the scales on strips of white celluloid, which gave a much greater distinctness in reading. The material was almost universally adopted, and the slide rules made by such firms as Nestler attained a high degree of perfection.
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