This is a fuel cell ammeter used in the Gemini program. With a 0-20 ampere scale, it monitored the current coming from the fuel cell. Fuel cells provided the electrical power in Gemini V and VII through XII. This ammeter was not flown in space.
Weston Instruments made the artifact and NASA transferred it to the Smithsonian in 1972.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.