  One year of Z- and WW-Threshold running of TESLA can provide the possibility
to measure electroweak precision observables to an extremely high accuracy. At
the Z peak O(10^9) Z bosons and about 6 10^8 b quarks can be collected. We
employ the expected uncertainties \Delta MW = 6 MeV and \Delta sin(theta_W,eff)
= 0.00001 and demonstrate in this way that very stringent consistency tests of
the Standard Model and the Minimal Supersymmetric Standard Model will be
possible. The indirect determination of the Higgs-boson mass within the
Standard Model can reach an accuracy of about 5 %. The 6 10^8 b quarks can be
used to investigate various b physics topics.
