The FG5 absolute gravimeter is a high precision, high accuracy, transportable instrument that measures the vertical acceleration of gravity (g).
The operation of the FG5 is simple in concept. A test mass is dropped vertically by a mechanical device inside a vacuum chamber, and then allowed to fall a distance of about 20 cm.
The FG5 uses a laser interferometer to accurately determine the position of the free-falling test mass as it accelerates due to gravity. The acceleration of the test mass is calculated directly from the measured trajectory.