Altimeter
From Memory Alpha, the free Star Trek reference.
An altimeter is an instrument used to measure the altitude to a fixed level.
In 2254, the Talosians scanned the library computer banks, including a diagram of the Ranger 3 United States space probe. Among the equipment noted on the diagram were radio antennae, including a high-gain transmitter antenna; the lunar capsule and mid-course motor, retro-rockets, solar energy panels, a RADAR altimeter and gamma ray spectrometer. (TOS: "The Cage")
