The invention involves an apparatus and method for calculating characteristics of materials, such as equivalent strain, using an indenter where the method used is independent of indenter geometry. The method includes performing a scratch test to calculate the strain for each of a plurality of indenter shapes, such as a theoretical sphere and cone, using known equations. The strain of a composite indenter, such as a cone with a rounded tip, can then be determined taking into account contributions from each of the plurality of theoretical shapes.