# Specifying system of units in equation

A common way of specifying which system of units (e.g. SI, esu, CGS - not the units themselves, e.g. kg, J, K) an equation is written in, is adding the name of the system within brackets to the right in the equation. Example: Is there a standard/recommended way of doing this in LaTeX? I tried looking in siunitx and googling around, but I cannot find anything of relevance...

• What precisely are you asking? How to right align part of an equation environment? – Seamus Apr 6 '16 at 15:53
• I'm asking if there is a standard way of writing the system of units in an equation in TeX. If not, I just want to know the recommended way of right-aligning text in an equation. – fromGiants Apr 11 '16 at 10:13

I can suggest two ways:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{align}
\vec{\nabla} \times \vec{B} &= \mu_0\vec{j}          && \textup{(SI units)} \\
\vec{\nabla} \times \vec{B} &= \frac{4\pi}{c}\vec{j} && \textup{(CGS units)}
\end{align}

\begin{alignat}{2}
\vec{\nabla} \times \vec{B} &= \mu_0\vec{j}          &\qquad& \textup{(SI units)} \\
\vec{\nabla} \times \vec{B} &= \frac{4\pi}{c}\vec{j} &&       \textup{(CGS units)}
\end{alignat}

\end{document} • The alternative of pushing the labels next to the equation numbers doesn't really appeal me (it can be done with flalign). – egreg Apr 6 '16 at 16:52