Anton Paar has published an application note on the use of Frequency Sweep to measure the Zero-Shear Viscosity.
The report explains why the Frequency Sweep is considered the favoured method, as it provides accurate results and additional information about the molecular structure and the visco-elastic properties of a sample (storage modulus and loss modulus as well as damping factor).
In the same report, the zero-shear viscosity is calculated using the Carreau-Yasuda regression, a very practical approach for getting an average value for the relaxation time of a measured polymer sample and the Zero-Shear Viscosity which is needed for the molar mass calculation.
