  We use IGETS absolute gravitational acceleration measurement data to study
the gravitational acceleration variance. The relative variance of $\delta g /g$
in 22 years is less than $4\times 10^{-8}$. Since $\delta G /G\lessapprox\delta
g /g $, this implies the relative variance of Newtonian constant is less than
$3\times 10^{-9}$ based on an sine-like oscillation hypothesis. This limit is
at least 4 orders of magnitude better than the existing $G$ measurements. The
scattered values of reported $G$ measurements coming from different experiments
are most probably coming from systematic errors associated with these
experiments and not due to intrinsic time variation of $G$. We also find that
$\dot{ G} /G<5.61\times 10^{-10} \text{yr}^{-1}$ based on a linear hypothesis.
This is the best terrestrial result so far.
