The electromagnetic field strength tensor is given by F μ μ ν ν = [ 0 − − 1 c E x − − 1 c E y − − 1 c E z 1 c E x 0 − − B z B y 1 c E y B z 0 − − B x 1 c E z − − B y B x 0 ] (SI units, signature ( + , − − , − − , − − ) ) . in SI units. In relativity, the Gaussian system of units is often preferred over SI units, even in texts whose main choice of units is SI units, because in it the electric field E and the magnetic induction B have the same units making the appearance of the electromagnetic field tensor more natural. Consider a Lorentz boost in the x -direction. It is given by Λ Λ μ μ ν ν = [ γ γ − − γ γ β β 0 0 − − γ γ β β γ γ 0 0 0 0 1 0 0 0 0 1 ] , F μ μ ν ν = [ 0 E x E y E z − − E x 0 B z − − B y − − E y − − B z 0 B x − − E z B y − − B x 0 ] (Gaussian units, signature ( − − , + , + , + ) ) , where the field tensor is displayed side by side for easiest possible reference in the manipulations below.