Usually yes, the frequency in the electric grid is pretty stable but .. .. it's not really precise 50Hz, just +/- 50Hz. .. there are more than just proof of c

Usually yes, the frequency in the electric grid is pretty stable but .. .. it's not really precise 50Hz, just +/- 50Hz. .. there are more than just proof of concepts, you can tell from a video, when it was made from the backround noise from the main grid. https://www.umiacs.umd.edu/publications/seeing-enf-natural-time-stamp-digital-video-optical-sensing-and-signal-processing https://www.umiacs.umd.edu/publications/seeing-enf-natural-t... .. a few years ago, was the European electric network several minutes to late, because not every country did pay for the electric power. https://www.nationalgeographic.com/science/article/european-clocks-six-minutes-late-serbia-kosovo-electricity-grid-spd https://www.nationalgeographic.com/science/article/european-...