Progress on the CLEO II CsI Electromagnetic Calorimeter

The upgrade of the CLEO general purpose magnetic detector at CESR includes a new high resolution CsI crystal electromagnetic calorimeter situated in a 1.5T magnetic field. The scintillation light from the CsI is detected by photodiodes. We report on progress made in understanding both the theoretically and experimentally obtainable energy resolution. We give test results on full size crystals from exposure to radioactive sources and a 180 MeV e+ beam.