Hitherto the quantification of material properties of a material submitted to a deformation has been taken as a function of one or more internal variables. When making measurements of yield properties as a function of a deformation a convenient way of describing the deformation in an experiment is to describe the total strain history as a curve in the 6-dimensional shear strain, normal strain space. In order to be able to use these experimental data for calculation, the development of this strain curve must be transformed into a set of scalar relations that may be used for predicting the yield surface at a given point in a new strain history. A simple example of this concept is to take the length of the strain curve as describing scalar relation: E.g. to use the equivalent strain as parameter for describing the yield stress. This paper focuses on the strain curve concept and the possibilities to convert this curve into useful scalar relations from experimental data.The strain history for plane strain when assuming volume constancy may be plotted in a shear strain, normal strain diagram, which has the property of showing both the rotation of principal deformation axes during the deformation and the amount of accumulated equivalent strain. This strain diagram makes the basis for the development of concepts for converting the strain path curve into scalar variables.