The decay scheme on the left shows that Hg produces a continuous beta spectrum with maximum energy 214 keV, that leads to an excited state of the daughter nucleus Tl. This state decays very quickly (within 2.8×10 s) to the ground state of Tl, emitting a gamma quantum of 279 keV.
The figure on the right shows the electron spectrum of Hg, measured by means of a magnetic spectrometer. It includes the continuous beta spectrum and K-, L-, and M-lines due to internal conversion. Since the binding energy of the K electrons in Tl is 85 keV, the K line has an energy of 279 - 85 = 194 keV. Due to lesser binding energies, the L- and M-lines have higher energies. Due to the finite energy resolution of the spectrometer, the "lines" have a Gaussian shape of finite width.