\(T = 2\pi \sqrt {\frac{{{r^3}}}{{Gm}}} \,\,\,\,\,\,\,{T^2} = \frac{{4{\pi ^2}}}{{GM}}{r^3}\)
Relative uncertainty in the mass of the earth
\(\left| {\frac{{\Delta M}}{M}} \right| = 2\frac{{\Delta T}}{T} = 2 \times {10^{ - 2}}\)
\(\left( {4\pi \ G constant and relative uncertainty
in radius \frac{{\Delta r}}{r}} negligible \right)\)