Ok one last attempt before I leave Plato's cave.
The youtube source you have there is just some random internet guy pointing out that it is hard to reproduce Cavendish's experiment especially when using improper equipment. That tiny little reproduction shown is nothing like the setup Cavendish used.
https://www.aps.org/publications/apsnews/200806/physicshistory.cfmHe (Cavendish) considered the problem for years, until in 1797, at age 67, he began his own experiments. He started with a torsion balance apparatus given to him by his friend, the geologist Reverend John Michell, who had been interested in doing the experiment himself but wasn’t able to carry it out before he died. Realizing that Michell’s equipment was inadequate to measure the tiny gravitational force between two small metal spheres, Cavendish set about tinkering until he had a more precise setup.
He built a large dumbbell, with two-inch lead spheres stuck to the ends of a six-foot long wooden rod. The rod was suspended from a wire held at the center, and was free to rotate. A second dumbbell with two twelve-inch lead spheres weighing 350 pounds each was then brought near the first so that the large spheres would attract the smaller ones, exerting a slight torque on the suspended rod. Cavendish would then painstakingly watch for hours to observe the rod’s oscillations.
This would provide a measure of the gravitational force of the larger spheres on the smaller ones. And since the density of the spheres was known and the gravitational attraction between Earth and the spheres could be measured by weighing the spheres, the ratio the two forces could be used to determine Earth’s density.
Since the gravitational force between the spheres is so weak, the tiniest air current could ruin the delicate experiment. Cavendish placed the apparatus in a closed room to keep out extraneous air currents. He used a telescope to observe the experiments through a window, and set up a pulley system that made it possible to move the weights from outside. The room was kept dark to avoid temperature differences in different parts of the room affecting the experiment.
Cavendish relentlessly tracked down potential sources of error. He rotated the spheres in case they had picked up some magnetization. He observed the attraction of the rods without the spheres on the ends. He tried different types of wire to support the apparatus.
After agonizing over every possible complicating factor, Cavendish finally reported his results in June 1798 in a 57-page paper in the Transactions of the Royal Society entitled “Experiments to Determine the Density of the Earth.” He reported that the density of Earth was 5.48 times the density of water. (The currently accepted value is 5.52).
Others later repeated the experiment, using similar apparatus, and for almost a century no one achieved any improvement over Cavendish’s original measurement.
But you do not need to believe Cavendish his experiment is just the one you can do on your own. More recently they measured the Newtonian constant of gravity, G, using a gravity gradiometer based on atom interferometry (link below)
http://science.sciencemag.org/content/315/5808/74.abstractAnd here is a discussion and review article on the multiple experimental measurements of G.
http://iopscience.iop.org/article/10.1088/0034-4885/60/2/001/meta;jsessionid=0E38B9AAAC8E1E96A924A79A08A8FB05.c3.iopscience.cld.iop.org