If the electron is visualized as a classical rigid body in which the mass and charge have identical distribution and motion that is rotating about an axis with angular momentum L, its magnetic dipole moment μ is given by: μ μ = − − e 2 m e L , where m e is the electron rest mass. The angular momentum L in this equation may be the spin angular momentum, the orbital angular momentum, or the total angular momentum. The ratio between the true spin magnetic moment and that predicted by this model is a dimensionless factor g e, known as the electron g -factor : μ μ = g e ( − − e ) 2 m e L .