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 alpha, beta and gamma 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 alpha, beta and gamma the values appropriate to each system.