(a) The power-grid frequency measures the balance of generation and load. (b) Synchronised power-grid frequency measured at different locations in the Continental European grid from July 2019. We observe a strong decrease in the power-grid frequency at 22:00 due to a rapid de-ramping of power generation. The inset shows a magnification of the time series for a 90-second interval. The frequency is almost the same for all locations in the grid; residual differences are damped out on the time scale of seconds. (c) The frequency in a microgrid at the main campus of the University of the Free State in South Africa. The microgrid operates close to the nominal frequency of 50 Hz. The actual frequency decreases after a loss of power in the municipality.