Calibrating the CMS Electromagnetic Calorimeter using $\pi^0$'s

Calibration defines the ultimate performance of the CMS electromagnetic calorimeter (ECAL) at the LHC. The individual calibration of all 75848 crystal channels to the desired precision of 0.5\% is a challenge. $\pi^0\to \gamma\gamma$ has a very large production rate and a substantial sample can be accumulated relatively easily. Here we present a study on calibrating this detector in-situ using inclusive $\pi^0$'s.