TTP99-37 Implications of Results from $Z$-- and $WW$--Threshold Running

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 times 10^8 b quarks can be collected. We employ the expected uncertainties Delta(M_W) = 6 MeV and Delta(sin^2 theta_eff) = 0.00001 and demonstrate in this way that very stringent consistency tests of the Standard Model (SM) and the Minimal Supersymmetric Standard Model (MSSM) will be possible. The indirect determination of the Higgs-boson mass within the SM can reach an accuracy of about 5 %. The 6 times 10^8 b quarks can be used to investigate various b physics topics.