# why there is no accuracy of the measured value of $G$?

With the advancement of Modern Technology still there is no accuracy of the measured value of $G$ Gravitational Constant, why!?

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①Gravitation is too small.②The prototype limits the accuracy of mass measurement.③Gravitation of unwanted sources (equipment, lab, you) cannot be screened. –  C.R. Sep 4 '12 at 0:32
What does "no accuracy" mean? –  Ben Crowell Aug 14 '13 at 4:25

With all due respect, I think both of these answers are way out of date. Read item 4 here http://www.npl.washington.edu/eotwash/experiments. Systematic errors associated with the torsion fibers commonly used made the bias much larger than the standard error. The U Wash group developed a feedback torsion balance which virtually eliminated anelasticity. It's still a hard measurement, but at least we are beyond the embarrassment of several reputable measurement whose 95% CI's didn't overlap. Having a torsion balance in which feedback keeps the fiber from moving is pretty sweet. I have no connection with the EotWash group.

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