  The ATLAS Muon Spectrometer is designed to measure the momentum of muons with
a resolution of dp/p = 3% and 10% at 100 GeV and 1 TeV momentum respectively.
For this task, the spectrometer employs 355,000 Monitored Drift Tubes (MDTs)
arrayed in 1200 Chambers. Calibration (RT) functions convert drift time
measurements into tube-centered impact parameters for track segment
reconstruction. RT functions depend on MDT environmental parameters and so must
be appropriately calibrated for local chamber conditions. We report on the
creation and application of a gas monitor system based calibration program for
muon track reconstruction in the LHC startup phase.

Instrumentation and Detectors;High Energy Physics - Experiment