\section{Introduction}
\label{sec:eudet}

DECAL concept described elsewhere. Sensor developed in context of ILC.
Main uncertainty due to lack of very high granularity shower data.

Current paper describes first measurements of EM showers with a highly
granular detector. Data taken at CERN HB6 North Area beam in Sept 2010.
Data takes consisted of muons
from XXX to YY\,GeV and electrons with from XXX to YY\,GeV. Detector used
was EUDET telescope with tungsten inserted between the planes of
sensors to produce EM showers.

In this paper, section~\cite{sec:eudet} contains a description of the
equipment used for these measurements. Section~\cite{sec:tracks} describes
the performance of the telescope with single charged particles. It also
gives details of the simulation developed for the sensor response. The
data taken with electromagnetic showers are described in 
section~\cite{sec:showers}, which includes a comparison of the
shower densities with simulation. Finally, section~\cite{sec:conclusions}
gives the conclusions from these studies.

\section{The EUDET telescope}
\label{sec:eudet}

The EUDET telescope is a six-layer silicon sensor device which is available
as a multi-purpose facility. The telescope was developed as part of the
EUDET project~\cite{ref:eudet:eudet} and details of the telescope design can be
found in~\cite{ref:eudet:telescope}. A description of the main features of
the telescope relevant to this paper are given below.

\subsection{Sensors}
\subsection{Telescope layout}
\subsection{Data acquisition}
\subsection{Tungsten absorber}

\section{Single track measurements}
\label{sec:tracks}

\subsection{Data taken}
\subsection{Simulation model}
\subsection{Tuning simulation parameters}
\subsection{Comparison of cluster sizes and positions}
\subsection{Comparison of cluster resolutions}

\section{Electromagnetic shower measurements}
\label{sec:showers}

\subsection{Data taken}
\subsection{Measurement of shower density}
\subsection{Comparison with simulation}

\section{Conclusions}
\label{sec:conclusions}
