“…Measurements of α s obtained at different energy scales can be compared, either by evolving backwards to the point Λ where α s diverges, or by evolving to a common reference energy, which in recent years has become the Z mass. In the evolution [1] α s is continous at flavour thresholds, which, within the still comparatively large uncertainties of the quark masses, can be taken at the MS-running mass of the respective quark flavour. As an example consider the evolution of an α s -measurement with n f = 3 from the scale µ = m τ to µ = M Z .…”