Faber Castell-stahlbeton 2/31 concrete slide rule full set 1973 Germany

This full set of slide rule, manual, plastic sheet and container are made by Faber-Castell from Germany. This model is the rare 2/31 Stahlbeton Duplex. It has special scales on front for concrete calculations as well as a spectacular cursor, on the back it has a scale set for more standard calculations. Everything is complete and in good condition including the rubber feet. There are signs of use and age (mostly yellowing between the lines), priced accordingly. The case is also complet and marked, some writing in pencil on the German instructions manual (dated 1973). 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!