Calibration of the ATLAS Muon Chambers

The high-pressure drift tube chambers for the muon spectrometer of the ATLAS detector at the LHC have to provide a track position resolution of 40~$mu$m. The chambers consist of two triple or quadruple layers of drift tubes of 30~mm diameter with a average spatial resolution of 80~$mu$m. The precise knowledge of the space-to-drift-time relationship $r(t)$ to better than 20~$mu$m is mandatory. It has to be recalibrated every few hours during ATLAS data taking using muon tracks from a dedicated data stream. The data of the stream will be processed at three calibration centres such that a new drift chamber calibration will be provided within a few hours after data taking. We shall present the drift-chamber calibration concepts, the key features of the calibration algorithms, and the results of the calibration of cosmic muon data recorded by the ATLAS detector.