\chapter{Some chapter}
This is a chapter.

\section{1}
\label{sec:1}
\begin{equation}
  \label{eq:1}
  1
\end{equation}

\section{2}
\label{sec:2}
\begin{equation}
  \label{eq:2}
  2
\end{equation}

\section{3}
\label{sec:3}
\begin{equation}
  \label{eq:3}
  3
\end{equation}

