Nestler 39 system Besser Electro pocket slide rule Germany 1920

Very small, very early version of this unusual nr. 39 slide rule. It is an electro slide rule for the engineer that worked with early electrics. It uses a system Besser, invented by Erwin Besser. It has special scales on both sides of the slide as well. It is so early that I does not carry a number in the stock and it is completely square shaped, made from partially lacquered mahogany and only measures ca. 15 cm or 6 inches (later wooden pocket model are longer). It is all complete and in great condition, including the additional information on the back and the original signed card board box (little faded). Do check the video below on how to work your vintage man tool : slide rule operation instructions!