HW Helper P: 6,202 You know that $$T=2\pi \sqrt{\frac{l}{g}}$$ so that $$T^2=4\pi^2 \frac{L}{g}$$ and that means that $$g=\frac{4\pi^2}{T^2}L$$ To find the error you do this. $$\frac{\delta g}{g}=2\frac{\delta T}{T} + \frac{\delta L}{L}$$ $\delta T$ would be the error in T and similarly for $\delta L$ is the error in L.