This set of slide rule and box are from Aristo from Germany. This model is the rare 939 Stahlbeton Duplex – Ahrend 702. It is also marked with a Dutch Comapny name: Torstaal N.V. Den Haag (The Hague). It has special scales on both sides as well as a spectacular cursor. 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!