US navy vertical aerial photography bildflug airplain slide rule Felshental 1960 USA

This is a US Navy duplex slide rule used for calculating condition for arial photography aka taking pictures out of airplanes (vertically / straight down). Used only for army purposes in the 1960’s. This one was made by Felsenthal for the US military. I assume the original manual was part of the pilot study books, but it does come with an original sheet of homework from the U.S. Naval Intelligence school- Air devision….giving it a clear pedigree as well as good indications of how it works (answers to the 20 questions provided in writing). It comes in the original non signed vinyl sleeve as well. The slide rule is in very good condition with minimal signs of use, it measures ca. 13,5 cm or 5 1/4 inches in diameter. Check the attached video on how to work your vintage man tool : slide rule operation instructions! And also make sure to check the German straight Aristo Bildflug version as well.