oscillometer

from The Century Dictionary.

• noun A device for indicating and measuring the rolling of a ship. It consists of a motor-driven gyroscope mounted in gimbals, which maintains its absolute plane of rotation in space and, by the movement of pointers along scales attached to the frame, shows the angular departure of the vessel from the vertical.

from the GNU version of the Collaborative International Dictionary of English.

• noun An instrument for measuring the angle through which a ship rolls or pitches at sea.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun physics, medicine Any of several devices that measure oscillations
• noun nautical A device that measures the roll (or pitch) of a ship