The Newtonian constant of gravitation -known in the finely tuned business of metrology as 'big G' - has come a long way since British physicist Henry Cavendish first measured the gravitational attraction of Earth in 1798. Although G derived from Cavendish's measurements had an uncertainty of about 1%, modern measurements have tightened that to just a couple of tens of parts per million.rnBut the relentless honing of G may have hit a stumbling block. Two recent experiments are in striking disagreement with earlier findings, and the overall uncertainty in the value of the constant may be set to increase.
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