Air duct calculator 1/77 Luftkanäle slide chart 1960 Germany

This is a very specific slide rule chart for calculating flow through air ducts and pipes. It is marked 1/77 and specially made for the Reku Keramchemie from Germany. It is in complete and working with small signs of use and age. There is also a later version as a bonus (5/77 for the Weiss Compay), because it has tears but still functions, so more for reference. Both come in one leather sleeve (marked Weiss). It measures ca. 22 cm or ca. 9 inches wide. Check the attached video on how to work your vintage man tool : slide rule operation instructions!