  The drift velocity in drift tubes of the CMS muon chambers is a key parameter
for the muon track reconstruction and trigger. It needs to be monitored
precisely in order to detect any deviation from its nominal value. A change in
absolute pressure, a variation of the gas admixture or a contamination of the
chamber gas by air affect the drift velocity. Furthermore, the temperature and
magnetic field influence its value. First data, taken with a dedicated Velocity
Drift Chamber (VDC) built by RWTH Aachen IIIA are presented. Another important
parameter to be monitored is the pressure inside the muon drift tube chambers.
The differential pressure must not exceed a certain value and the absolute
pressure has to be kept slightly above ambient pressure to prevent air from
entering into the muon drift tube chambers in case of a leak. Latest drift
velocity monitoring results are discussed.
