This set of slide rule and box are from Aristo from Germany. This model is the rare 939 Stahlbeton Duplex – Ahrend 702. It has special scales on both sides as well as a spectacular cursor. Also the extra tabel is included. Used for calculations for reinforced concrete according to the Göttsch system. Everything is complete with some signs of use and age. It measures 33,5 cm or 13 1/4 inches. Check the attached video on how to work your vintage man tool : slide rule operation instructions!