A Combination of CDF and D0 Results on the Mass of the Top Quark
  We summarize the top-quark mass measurements from the CDF and D0 experiments at Fermilab. We combine published RunI (1992-1996) measurements with the most recent RunII (2001-present) measurements using up to 2/fb of data. Taking correlated uncertainties properly into account the resulting preliminary world average mass of the top quark is Mt=172.6 +/- 0.8(sta) +/- 1.1(sys) GeV/c2, assuming Gaussian systematic uncertainties. Adding in quadrature yields a total uncertainty of 1.4 GeV/c2, corresponding to a relative precision of 0.8% on the top-quark mass. 
Tevatron Electroweak Working Group (for the CDF and D0 Collaborations)