Example of the power-law spectral fitting process (J1653+3945, also known as Mrk 501, on July 28, 2021). The magenta squares indicate the raw data, uncertainties are not shown to enhance readability. For every frequency, where more than one raw flux density value was available, the flux densities were averaged (black dots). The averaged flux densities were then fitted with a power-law spectrum (blue line). In the presented case, we found α = −0.262 ± 0.021.