Dennert und Pape (Workshop for Mathematical Instruments).
In 1863. the founders (Johann Christian Dennert and Martin Pape) started in Hamburg, Germany, and then moved to Altona, Prussia. Their original business consisted of 'Theodolites, Levels, Leveling Rods, Planimeters, Drawing Instruments and Scales with any graduation, made of ivory, brass, nickel silver, or silver-plated brass'. In 1872, they produced their first boxwood slide rules, and changed their name to Dennert & Pape, Mechanical-Mathematical Institute.
In 1879, they introduced brass body slide rules, and in 1886 were granted their patent (DRP 34583) for wooden rules with celluloid scales. In 1888 they switched from boxwood to mahogany bodies for their rules. In 1902, Max Rietz designed the slide rule scale arrangement that would live on under his name for the next century, 'System Rietz'. In 1924, the DUPA trademark was introduced for their products. Prof. Dr. Alwin Walther (from the Institute for Applied Mathematics, Technical University, Darmstadt) developed a new scale arrangement based on the 'Rietz' design with added log log scales, and the 'Darmstadt' model was born. It is significant that these designs literally became standards for all production in Europe, and were more conceptually advanced and better organized than most north american scale designs.
In 1936, D & P mahogany body rules were discontinued, and production changed to engineering plastics with the trademarks Astralon and Plexiglas. The new trademark, ARISTO, was also introduced for anything made with these new plastic materials, while other traditional tool designs continued to be marked as Dennert & Pape. In 1937, the Altona location became part of Hamburg, and the DR-2 flight computer designed by Plath, and made of plastic materials, was produced. Military products were marked with 'gwr' starting in 1942, and have no company identification. Due to wartime shortages, production was almost stopped in 1945, and remained weak until 1948, when the company was re-organized, and then marketed under the name ARISTO.