Nestler 21a Darmstadt 23″ 58cm long slide rule 1940 Germany

This is a beautiful large slide rule using the Darmstadt system with number 21a. Due to the length it is more accurate than the standard model 21. I am guesstimating this one is from ca. 1940 since there are screws in the ends. Everything is complete, no cracks, chips or dings and in working condition and very large glass cursor with 1 large and 2 small hairlines. There are some signs of normal use and hardly any signs of age (small scratch on the top edge laminate). The cursor is in very good condition and two small pointers for the scales on the side of the slide rule. Overall in a great condition. There are marks from storage on the corners of the original signed cardboard container as well as a period piece of tape. It measures about 58 cm or 23 inches wide. Check the attached video on how to work your vintage man tool : slide rule operation instructions!