A method for adjusting the centre of mass of a freely falling body in absolute gravimetry

In absolute gravimeters, rotation of the falling body causes a systematic error. This error can be minimized by coinciding the centre of mass (COM) of the body with its optical centre (OC). A method to measure the distance between these centres in 3D space is described. The method is based on a mechanical balancing technique. Using this method, the COM of a hollow corner cube mirror assembly is adjusted to the OC to within (43 ± 16) µm. An uncertainty budget is given.