Using viscous relativistic hydrodynamics we show that systematic studies of
the impact parameter dependence of the eccentricity scaled elliptic flow can
distinguish between different models for the calculation of the initial source
eccentricity. This removes the largest present uncertainty in the extraction of
the specific viscosity of the matter created in relativistic heavy-ion
collisions from precise elliptic flow measurements.Comment: 4 pages, incl. 4 figure