Addiphot log system H.C. Lange slide rule exposure meter 1940 Germany

This interesting instrument comes in a full set of slide rule, manual in German) and leather sleeve. It is somewhat unusual a a slide rule since it has no cursor but you have to look through it to calculate / find the value needed. It has a see-through part which by gets darker when sliding the central part. It is a system from Germany by mr. H.C. Lange. It is one of the smallest slide rule types I have seen since it measures only ca 6 cm or 2 1/4 inches in height. Check the video on how to work your vintage man tool : slide rule operation instructions!