The lead glass shower calorimeter consists of four stacks of TF1 leaded glass (similar to SF1). Each stack contains thirteen blocks for a total of 52 blocks. The blocks are 10 cm by 10 cm by 70 cm and all are read out by a PMT at one end at least. Currently the two layers have PMT readout at both ends.
High energy particles emit Cerenkov radiation when passing through the glass and a signal is collected that is proportional to the sum of the path lengths travelled by all the particles which are above the threshold for Cerenkov emission. High energy electrons will produce a large signal as they have a large bremsstralung cross section and the photons which are produced in the bremsstralung process have a large cross section to produce electron positron pairs (all of which will be above the Cerenkov threshold). This process of bremsstralung followed by pair production is called an electromagnetic shower.
The histograms associated with the calorimeter should be inspected regularly to assure that it is functioning properly.