Status of measurement of the Newtonian gravitational constant G

A precise knowledge of the Newtonian gravitational constant G has an important place in physics and is of considerable metrological interest. Although G was the first physical constant to be introduced and measured in the history of science, it is still the least well known. The 1998 CODATA recommended value for G, (6.673±0.010)×10^-11 m³ kg^-1 s^-2, has an uncertainty of 1500 parts per million (ppm), which is much larger than that of all other fundamental constants. Here we review the status of our knowledge of the absolute value of G, nine experiments for measuring the absolute values of G within the last five years, the experiments in progress and being planned, and the systematic error due to the inelasticity, the nonlinearity and the thermoelasticity of torsion fibre.