<p>A new set of two isochoric strain tensor invariants is introduced. One invariant directly indicates how close the isochoric deformation in a material point is to the homogeneous ideal modes used for material calibration experiments, which are uniaxial and equibiaxial tension and pure shear. The other invariant is a measure of the strain intensity. Here, strain states are assumed to be equally intense if the sum of the principal invariants is equal. The invariants were designed with the goal in mind to interpret the (second-order tensor) strain fields in design workflows for rubber parts in an easy way by contour plots of the scalar invariants. The new concept is compared to two other concepts from the literature that can be applied with a similar objective. Furthermore, a procedure is introduced to utilize the new concept to modify the material calibration in order to achieve better simulation results for a specific part. To this end, the calibration experiments in the ideal modes are given greater weight if the actually occurring strain states in the part under consideration are closer to them than to the other ideal modes, whereby the intensity of the strain states is also taken into account. The procedure is illustrated on the simple example of a sheared cylinder and was able to greatly improve the prediction of force-displacement curves in comparison with an equally weighted material calibration, which is assessed by a validation experiment of the actual rubber cylinder.</p>