This specialty slide rule was designed to aid those planning aerial photography, relating the aircraft's altitude, air speed, etc. with the desired area to be photographed. It would not have been used for the detailed deisgn of a mission, but it was a way for engineers and air crews to get a quick sense of the basic parameters of a mission. The device would have been useful for classified military as well as unclassified civilian applications.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.