The covariant formulation of Maxwell’s equations expressed in a form independent of specific units

The covariant formulation of Maxwell’s equations can be expressed in a form independent of the usual systems of units by introducing the constants α, β and γ into these equations. Maxwell’s equations involving these constants are then specialized to the most commonly used systems of units: Gaussian, SI and Heaviside–Lorentz by giving the constants α, β and γ the values appropriate to each system.