Calibration of CMS Electromagnetic Calorimeter at LHC startup

The first 7 TeV LHC collisions recorded with the CMS detector have been used to perform a channel-by-channel calibration of the electromagnetic calorimeter (ECAL). Decays of pi(0) and eta into two photons as well as the azimuthal symmetry of the average energy deposition at a given pseudorapidity are utilized to equalize the response of the individual channels. The ECAL comprises a central barrel section and two endcaps. Based on an integrated luminosity of similar to 100 nb(-1), a channel-by-channel in-situ calibration precision of 1.15% has been achieved in the barrel ECAL in the pseudorapidity region vertical bar eta vertical bar < 0.8. The energy scale of the ECAL has been investigated and found to agree with the simulation to within 1% in the barrel and 3% in the endcaps.