As of February 2007, the best measurement of the anomalous magnetic dipole moment of the electron was made by the group of Gerald Gabrielse at Harvard University, using a single electron caught in a Penning trap. The difference between the electron's cyclotron frequency and its spin precession frequency in a magnetic field is proportional to "g"−2. An extremely high precision measurement of the quantized energies of the cyclotron orbits, or "Landau levels", of the electron, compared to the quantized energies of the electron's two possible spin orientations, gives a value for the electron's spin "g"-factor: