\documentclass{article}
\usepackage[cfg=sample04.cfg]{nomencl}
\usepackage{siunitx}
\makenomenclature
\begin{document}
\section*{Main equations}
\begin{equation}
  a=\frac{N}{A}
\end{equation}%
\nomenclature{$a$}{The number of angels per unit
  area\nomunit{\per\square\meter}}%
\nomenclature{$N$}{The number of angels per needle point}%
\nomenclature{$A$}{The area of the needle
  point\nomunit{\square\meter}}%
The equation $\sigma = m a$%
\nomenclature{$\sigma$}{The total mass of angels per unit
  area\nomunit{\kilogram\per\square\meter}}%
\nomenclature{$m$}{The mass of one angel\nomunit{\kilogram}}
follows easily.
\printnomenclature
\end{document}
