Calibration of the Electromagnetic Calorimeter of the CMS experiment

The electromagnetic calorimeter (ECAL) of the CMS experiment is an homogeneous, hermetic detector with high granularity. Its potential performances are outstanding in terms of energy resolution, dynamic range and noise level. These characteristics make the calorimeter the most powerful device in the search of the decay in two photons of the Higgs particle. However, the energy resolution depends crucially on the channel to channel intercalibration precision. Therefore, great attention must be given to the calibration process. In this contribution we will describe the strategy that the ECAL group has devised to calibrate the detector. We will report on the pre-calibration processes that have already been performed, the strategies for intercalibration at startup and those foreseen when sufficient statistics will be accumulated to use W and Z events. For the normal data taking regime, an intercalibration precision of 0.5\% should be reached, while the response of the detector will be monitored regularly.