The use of modern viscometers ensures that the inertia of the measuring device in unsteady rheometry is taken into account. This is made possible by appropriate viscometer design, or by considering the transmission function during the recording of data. On the other hand the inertia of the fluid in general is neglected in the evaluation of experiments. This leads to errors in the determination of material functions for liquids with low‐shear viscosities, such as dilute polymer solutions. For shear oscillatory experiments evaluation methods are presented for cylindrical and plane Couette flow which yield the complex viscosity of linear viscoelasticity taking into account fluid inertia. For cessation or inception of steady‐shear flow one has to assume a specific constitutive equation for linear viscoelastic liquids in order to develop a correct evaluation method. Relations are presented for Maxwell and Jeffreys fluids. For more complicated models a numerical evaluation method is outlined.