system
Given the following post, respond as if you're commenting on Reddit:
human
How is the gravitational constant calculated ?
gpt
There are two main methods:

- Literally measure the minuscule gravitational force between artificial objects of known mass. The first determination of G was by this method, by Cavendish in 1798, 71 years after Newton had died. This technique is not precise because the force is extremely small and sources of error are everywhere.

- Use an estimate of the gravitational parameter `[;\mu = MG;]` of a certain astronomical bodies by studying the motion of other objects orbiting around it, and combine it with an independent estimate for the mass of the object based on other physical considerations. This technique is not precise because while `[;\mu;]` can be measured with great accuracy, `[;M;]`is basically most of the time pulled out of someone's ass, since it's not exactly trivial to guess the internal composition of a celestial body at the fifth decimal digit.

So this concludes why there is a large error on current estimates of G.