The basic principle of pulsed EPR and NMR is similar. Differences can be found in the relative size of the magnetic interactions and in the relaxation rates which are orders of magnitudes larger (faster) in EPR than NMR. A full description of the theory is given within the quantum mechanical formalism, but since the magnetization is being measured as a bulk property, a more intuitive picture can be obtained with a classical description. For a better understanding of the concept of pulsed EPR consider the effects on the magnetization vector in the laboratory frame as well as in the rotating frame. As the animation below shows, in the laboratory frame the static magnetic field B 0 is assumed to be parallel to the z-axis and the microwave field B 1 parallel to the x-axis. When an electron spin is placed in magnetic field it experiences a torque which causes its magnetic moment to precess around the magnetic field. The precession frequency is known as the Larmor frequency ω L.