Note 1 to entry: For events A, B, with position four-vectors $\left\{\text{j}{c}_0{t}_{\text{A}},x_{\text{A}},y_{\text{A}},z_{\text{A}}\right\}$ and $\left\{\text{j}{c}_0{t}_{\text{B}},x_{\text{B}},y_{\text{B}},z_{\text{B}}\right\}$ respectively, squared space-time distance is $s_{{}_{\text{AB}}}^2=-c_0^2{(t_{\text{B}}-t_{\text{A}})}^2+{(x_{\text{B}}-x_{\text{A}})}^2+{(y_{\text{B}}-y_{\text{A}})}^2+{(z_{\text{B}}-z_{\text{A}})}^2$.

Note 2 to entry: The coherent SI unit of squared space-time distance is metre squared, ${\text{m}}^2$.