Energy and Impact Point Reconstruction in the Cms Ecal (testbeam Results from 2003)

The Electromagnetic Calorimeter of the CMS detector at the LHC will consist of approximately 75,000 PbWO4 crystals and is designed to provide a very precise energy measurement in a high radiation environment. During a testbeam campaign in 2003, an electron beam was used to test the performance of a system consisting of two super modules (a total of 100 crystals). In this talk an overview of the various issues related to the reconstruction of the energy deposition in single crystals and the resolution on the impact position of incident particles is presented. The final energy resolution, using a proto-type of the final electronics meets the target specification.