The Lunar Traverse Gravimeter was designed to measure the Moon's gravitational field using a precise accelerometer. While on the Moon, astronauts would move the device to different locations and take readings of the graviational force.
This particular Traverse Gravimeter is the flight back-up unit for the Apollo 17 mission. It was transferred to the Smithsonian in 1975.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.