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

DECAL concept described elsewhere~\cite{ref:introduction:decal}.
Sensors developed for this application~\cite{ref:introduction:ichep},
\cite{ref:introduction:tpac}.
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 positive hadrons with momentum of
120\,GeV and positrons with momenta from 10 to 100\,GeV. Detector used
was EUDET telescope with tungsten inserted between the planes of
sensors to produce EM showers.

In the rest of this paper, 
section~\ref{sec:telescope} contains a description of the
equipment used for these measurements. Section~\ref{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~\ref{sec:showers}, which includes a comparison of the
shower densities with simulation. Finally, section~\ref{sec:conclusions}
gives the conclusions from these studies.
