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 \(\eta _{\infty }\) the limiting viscosity at infinite shear rate; \(\rm{[}\eta _{0}\rm{]}\) is the limit of intrinsic viscosity at zero shear.