For systems showing non-Newtonian behaviour when measured in steady simple shear, a coefficient $\eta$ equal to $\frac{\sigma }{D}$ at a given value of the shear rate $D$, where $\sigma$ is the stress; ${\eta }_0$ is the limiting viscosity at zero shear rate, and ${\eta }_{\mathrm{\infty }}$ the limiting viscosity at infinite shear rate; $\text{[}{\eta }_0\text{]}$ is the limit of intrinsic viscosity at zero shear.