\documentclass{article}
\usepackage[nocfg]{nomencl}
\makenomenclature
\begin{document}
\section*{Main equations}
\begin{equation}
  a=\frac{N}{A}
\end{equation}%
\nomenclature{$a$}{The number of angels per unit area\nomrefeq}%
\nomenclature{$N$}{The number of angels per needle point\nomrefpage}%
\nomenclature{$A$}{The area of the needle point}%
The equation $\sigma = m a$%
\nomenclature{$\sigma$}{The total mass of angels per unit area\nomrefeqpage}%
\nomenclature{$m$}{The mass of one angel}
follows easily.
\eqdeclaration{32}
\printnomenclature
\end{document}