More surprising is the magnetic dipole moment found for individual electrons. This moment, associated with the electronic property of spin, is defined as the Bohr magneton. where e/m is the electronic charge to mass ratio, 1.76 × 1011 coulomb/kg, and 2π ̄h is Planck’s constant, ̄h = 1.05 × 10−34 joule sec so that me has the units A − m2.