You even know what G is?? "has been measured"....no, it has been ESTIMATED...waaaaaaaaaaaaaay to different thing:
The accuracy of the measured value of G has increased only modestly since the original Cavendish experiment. G is quite difficult to measure, as gravity is much weaker than other fundamental forces, and an experimental apparatus cannot be separated from the gravitational influence of other bodies. Furthermore, gravity has no established relation to other fundamental forces, so it does not appear possible to calculate it indirectly from other constants that can be measured more accurately, as is done in some other areas of physics. Published values of G have varied rather broadly, and some recent measurements of high precision are, in fact, mutually exclusive.[3][6]
you know, google the thing and you can find interesting things besides the gagnman video stuff.
No, the formula was derived from observation and DEDUCED. In fact, the formula didnt explain the motion of the mercury so enter Einstein to solve the problem...get educated boy...