Calibration software for the ATLAS monitored drift tube chambers

High pressure monitored drift tube (MDT) chambers will be used as precision tracking detectors in the muon spectrometer of the ATLAS experiment at the LHC (Large Hadron Collider) at CERN. An accurate knowledge of the space-time relation is needed to reach the design average resolution of 80 microns. The MDT calibration software has been designed to extract the space-time relation from the data themselves, through the autocalibration procedure, to store and retrieve the relevant information from the conditions database, and to properly apply it to calibrate the hits to be used by the reconstruction algorithms, taking into account corrections for known effects like temperature and magnetic field. We review the design of the MDT calibration software for ATLAS and present performance results obtained with detailed GEANT4-based simulation and real data from the recent combined test beam.