Rheology is the study of the relationship between force and deformation and embodies the concepts of material elasticity and viscosity. Elasticity is the ability of a material to store deformational energy ie if and how a material regains its original shape after being deformed. Viscosity, on the other hand, is a measure of the ability of a material to resist flow and reflects the ability of the material to dissipate deformational energy through flow.   Rather confusingly, a material that displays ability to flow is behaving “viscously”. An applied force results in an exhibition of a combination of both  mechanisms, where one normally dominates. This is termed viscoelasticity.

A rheometer can quantify both characteristics as functions of applied stress, strain, temperature, time etc. parameters that can be measured are:
Flow - the measurement of shear viscosity by controlled stress and rate methodologies and using ramped and equilibrium shear regimes to access complete flow curves.

• Creep -the measurement of low shear flow measurement. Models such as the Voigt unit are used to model this behaviour.

Oscillatory testing – used to explore viscoelasticity in a non-destructive test designed for revealing the linear elastic limit and its characteristics for particular substances. Measurements reveal mechanical moduli, thixotropy and thermal changes in materials. The elastic and viscous stresses ere related to material properties through the ratio of stress to strain, the modulus. The ratio of the elastic stress to strain is the elastic (or storage ) modulus G' the ratio of the viscous stress to strain is the viscous (or loss) Modulus G". The complex modulus G* = G'+ G" reflects the contribution of both elastic and viscous components to the stiffness of the material. The complex viscosity is a measure of the material’s overall resistance to flow as a function of shear rate. The ratio of the viscous modulus to the elastic modulus is the tangent of the phase angle shift (theta) the stress and strain vectors. Thus, G”/G’= tan (theta) measures the damping ability of the
material.

Simultaneous multiple frequency sweeps (MultiWave) is a newer test mode to observe a sample at several oscillatory frequencies simultaneously, rather than sequentially. It is advantageous for materials that change during measurement so that, for example, the exact moment of gelation or curing can be identified by measuring tan  at several frequencies simultaneously.