Abstract: A test specimen is composed of an elastic part and a viscoelastic part. The elastic part is braced against a support. The viscoelastic part is connected to the elastic part and pulled to deform the elastic part, and in so doing itself undergoes deformation. The deformation of the elastic-viscoelastic test specimen is limited by a fixed abutment against which the viscoelastic part comes to abut. The increase of deformation is at that time terminated. Thereafter, the viscoelastic part relaxes and creeps. During such relaxation and creeping a first and thereafter a superimposed second holographic photograph of the external surface of the elastic part or of the viscoelastic part are made. The time interval between the two exposures is selected in accordance with a preselected equation for purposes of reproducibility of the test.