subject of choices for independent units, see John David Jackson. Classicalelectrodynamics Third. New York: Wiley. 1998: 154 [2015-03-07]. ISBN 0-471-30932-X
Chinese(页面存档备份,存于互联网档案馆))) Multivalued Fields in in Condensed Matter, Electrodynamics, and Gravitation, World Scientific (Singapore, 2008) (also available
by Max von Laue in his book (1921) Die Relativitätstheorie, p. 34, and translated by Harald Iro. A Modern Approach to Classical Mechanics. World Scientific