of the electromagnetic current operator between two on-shell states. Here u ( p i ) and u ¯ ¯ ( p f ) are 4-spinor solution of the Dirac equation normalized so that u ¯ ¯ u = 2 m e , and q μ μ = p f μ μ − − p i μ μ is the momentum transfer from the current to the electron. The q 2 = 0 form factor F 1 ( 0 ) = − − e is the electron's charge, μ μ = 1 2 m e ( F 1 ( 0 ) + F 2 ( 0 ) ) is its static magnetic dipole moment, and − − 1 2 m e F 3 ( 0 ) provides the formal definion of the electron's electric dipole moment. The remaining form factor F 4 ( q 2 ) would, if non zero, be the anapole moment.