Study of the performance of the NA62 Small-Angle Calorimeter at the DA$Phi$NE Linac

The measurement of $BR(K^+topi^+ ubar{ u})$ with 10% precision by the NA62 experiment requires extreme background suppression. The Small Angle Calorimeter aims to provide an efficient veto for photons flying at angles down to zero with respect to the kaon flight direction. The initial prototype was upgraded and tested at the Beam Test Facility of the DA$Phi$NE Linac at Frascati. The energy resolution and the efficiency were measured and are presented.