The measurement of the center of mass and the optical center in a freely falling body of absolute gravimetry

In absolute gravimeters, rotation of the falling body leads to inaccurate measurement of gravity. The error can be minimized by collocating the center of mass (COM) of the body with its optical center (OC). A method to measure the distance between these centers is necessary. The method is based on torsion pendulum device. This paper considers the falling body as a pendulum in the whole system and using a quadrature interferometer to interrogate its twist mode.