$\underset{\_}{\underset{\_}{A}}:=\left(\text{j}V/c_0\text{;}\overrightarrow{A}\right)$

where $V$is electric potential, $\text{j}$ is the imaginary unit, and $c_0$ is speed of light in vacuum

Note 1 to entry: The coherent SI unit of electromagnetic four-potential is volt second per metre, $\text{V}\cdot \text{s}\cdot {\text{m}}^{-1}$.