Recent results for the cross section of electron-positron annihilation intohadrons and for the decay rates of the Z boson and the T lepton into hadronsincluding corrections of order at are reviewed. The consistency between twovalues of c measured at vastly different energies constitutes a striking test ofasymptotic freedom and requires the proper matching conditions at charmand bottom thresholds. Combining the results from Z and T decays leadsto as (Mz) = 0.1198 ± 0.0015 as one of the most precise and presently onlyNNNLO result for the strong coupling constant. We report a recent determina-tion of as which is based on a lattice evaluation of the pseudoscalar correlatorfor the charm quarks combined with continuum perturbation theory.
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