Impact of ATLAS electromagnetic calibration on precision measurements

Since the discovery of the Brout-Englert-Higgs boson a lot of effort has been devoted to the measurement of its properties. One of its key parameter is its mass, which has been measured by the ATLAS detector at the LHC. It required a big effort of calibration of the ATLAS electromagnetic calorimeter. The details of this calibration as well as the understanding of the detector it lead to will be described. The measurement of $m_H$ and how it has been impacted by the calibration will be described too.