# Redefine a given unit in siunitx

I would like to redefine the electron mass unit in siunitx so that it is \mathrm{m}_0 instead of the default \mathrm{m}_\mathrm{e}. How do I do that?

• \DeclareSIUnit{\Electronmass}{\mathrm{m}_o} and \si{Electronmass} – user11232 Nov 28 '14 at 10:17

The definition of \electronmass is

\DeclareSIUnit{\electronmass}{\text{\ensuremath{m_{\text{e}}}}}


Just change it.

\documentclass{article}
\usepackage{siunitx}

\DeclareSIUnit{\electronmass}{\text{\ensuremath{m_{0}}}}

\begin{document}
\SI{2}{\electronmass}
\end{document}


However, you must realize you're changing a standard symbol. And this shouldn't be done.

• Even if I do not change a standard symbol and give it another name, your approach looks weird when I have an exponent for my unit, e.g. $\SI{2}{\electronmass^2}$ (the original symbols have that too...). Is that intentionally (and by this I mean should it be that way due to some convention)? – DaPhil Dec 1 '14 at 7:22