  At a linear collider of the next generation the large event rates expected
from Bhabha and M\o ller scattering may be used to determine simultaneously
sin^2\theta_w and the polarization of both beams with very high accuracy. These
measurements can be performed in parallel to the other tasks of the linear
collider as a free by-product. A high degree of polarization and a good polar
angle coverage of the detectors turn out to be major assets.
