First put the sample in a certain way between the magnets of the spectrometer. Choose a suitable microwave frequency. Turn on the magnetic field and tune it over a range of values, while measuring the spectrum. At the value of the field where we have “resonance” of the EPR transitions, we will see peaks. From the value of the field we get from this, we can calculate the g factor. Due to anisotropy, the g “factor” is actually a tensor. This way we find the principle components of the g tensor, for a certain orientation of the field wrt the sample. We rotate the sample (or rotate the field if possible) to do the same measurements at different angles. Putting all data together leads to the shown pictures.