The S matrix ansatz is a rigorously model independent approach to desc
ribe the cross-sections and asymmetries in e+ e- annihilation. Using t
he cross-sections and asymmetries measured with the L3 detector during
the 1990 and 1991 running period, we determine the mass and the width
of the Z boson, the contributions of the Z exchange and of the gammaZ
interference. Including the polarization of the tau lepton in the ana
lysis, the leptonic helicity amplitudes of the scattering process are
determined assuming lepton universality. The results are compared with
other model independent ansatzes as realized in ZFITTER. A systematic
bias of the Z mass due to the gammaZ interference term is detected, w
hich leads to an underestimation of the error on m(Z) for model indepe
ndent determinations.