IceTop tank response to muons

Each digital optical module (DOM) of the IceTop air shower array is calibrated by identifying and understanding its muon response, which is measured in vertical equivalent muon (VEM). Special cal- ibration runs and austral season measurements with a tagging telescope provide the basis for determining the VEM and monitoring its variation with time and temperature. We also study muons that stop and de- cay in the tank. The energy spectrum of the electrons from muon decay is well known (Michel spectrum) and can also be used as a calibration tool. Both spectra are compared to a GEANT4 based Monte Carlo simulation to gain a better understanding of the tank properties.