The preshower and electromagnetic calorimeter, currently used in NOMAD,
are needed to recognize and reconstruct electrons and photons produced in the last emulsion
stacks.
The calorimeter is made of 875 lead glass blocks each 19 radiation lengths deep and with a
rectangular cross-section of 
.
It is preceded by a preshower consisting of two planes of proportional tubes following a
thick 
lead-antimony converter.
The preshower provides a better position measurement of photons converting in the lead and
electron-pion discrimination based on the early shower development technique.
The preshower consists of 286 horizontal and 288 vertical tubes made of extruded aluminium
profiles.
Each tube has a cross-section of 
and a wall thickness of 1 mm
and is strung
with a 30 
gold-plated tungsten anode wire held at a tension of 1500 V.
The tubes use an 80-20 
mixture.
The variation of the preshower gain with temperature and pressure is monitored using the
pulse height of straight through muons.
The lead glass counters (of type TF1-000) have to operate in the magnetic
field perpendicular to the counter axis.
Each block is read by a tetrode with a typical gain of 40 optically
coupled to the back face of the block.
This face is cut at 
with respect to the counter axis, such that the
axis of the tetrode forms an angle of to the field direction.
This limits the signal reduction due to the effect of the magnetic field to 20 %.
Monitoring of the lead glass response is performed using two blue LED's for each block.
The energy resolution of the calorimeter was measured to be
where E is expressed in GeV.
It was also found to be linear to better than 1.5 % in the energy range 1.5 to 80 GeV.