This is an unflown example of the Stable Platform used to guide the Saturn V rockets, which launched missions to the moon and to Earth orbit between 1967 and 1975.
Markings on the device indicate that it was modified twice, in February 1973 and again in April, 1974, as Saturn flights were coming to an end. It therefore represents a very late version of the design.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.