The transverse energy (E_t) resolution can be obtained by using single particles impinging the calorimeter,nearly parallel  to the detector axis Z.
A good resolution in the E_t allows to increase the efficiency in the tau detection, where final states of the tauonic neutrino interaction are characterised by missing transverse energy.
Since only a single  view of the calorimeter was instrumented, the projection of the transverse energy  E_t^x  in the instrumented plane (XZ) has been measured.
The following figure shows the  E_t^x  distribution for 3 GeV pions (left); the relative resolution for 3 GeV pions is in good agreement with the Monte Carlo prediction .

The right part of the figure shows the Monte Carlo prediction for the fully instrumented calorimeter in  E_t  reconstruction.