Faber Castell 8/12 DELBAG Airfilter (Luftfilter in German) 12,5 cm 5″ circular slide rule as a full set. This unusual high quality slide rule was produced by Faber Castell for DELBAG from Germany. Made specifically for Airfilter installation. Above the DELBAG logo is a DBGM patent number 1 693 170. Beautiful construction where the inner ring runs through the hollow half that has several small windows on both sides . On the back there are instructions for use in German. It comes complete with the instructions and signed vinyl pouch. It is in great condition without cracks and minimal signs of use or age. It is fully functioning and the diameter of the slide rule is 12,5 cm or 5 inches. Check the attached video on how to work your vintage man tool : slide rule operation instructions!
