I imagine the scientists follow a procedure roughly as follows:
1. Load sample into EPR spectrometer on a rotating support.
2. Apply magnetic field, irradiate with microwaves and collect data.
3. Increment the rotation of the sample by some number of degrees and repeat step 2.
4. Collect data over 360 degrees, maybe again rotating around another axis.
5. Use data to calculate g-tensor components at each orientation.