Editing Sign convention (section)

== Other sign conventions ==

* The sign choice for [[arrow of time|time]] in frames of reference and proper time: '''+''' for future and '''−''' for past is universally accepted.
* The choice of <math>\pm</math> in the [[Dirac equation]].
* The sign of the [[electric charge]], [[electromagnetic tensor|field strength tensor]] <math>\, F_{ab}</math> in [[Gauge theory|gauge theories]] and [[Maxwell's equations|classical electrodynamics]].
* Time dependence of a positive-frequency wave (see, e.g., the [[electromagnetic wave equation]]):
** <math>\, e^{-i\omega t}</math> (mainly used by physicists)
** <math>\, e^{+j\omega t}</math> (mainly used by engineers)
* The sign for the imaginary part of [[Permittivity#Complex permittivity|permittivity]] (in fact dictated by the choice of sign for time-dependence).
* The signs of distances and [[radius of curvature (optics)|radii of curvature]] of optical surfaces in [[optics]].
* The sign of work in the [[first law of thermodynamics]].
* The sign of the weight of a [[tensor density]], such as the weight of the determinant of the covariant metric tensor.
* The active and [[passive sign convention]] of [[Electric current|current]], [[voltage]] and [[Electric power|power]] in [[electrical engineering]].
* A sign convention used for [[curved mirror]]s assigns a positive focal length to concave mirrors and a negative focal length to convex mirrors.

It is often considered good form to state explicitly which sign convention is to be used at the beginning of each book or article.