This paper describes the importance of measuring the absolute strain levels in materials for relaxation and composition determination. The general reliance on assumed lattice parameters of materials for internal reference is shown to create uncertainties. The underlying substrate can be distorted by epitaxy or from surface preparation and can therefore be an unreliable reference. Because of this, absolute strain measurements are preferable. Two absolute lattice parameter methods are compared and a new procedure for precision determination of relaxation described. It was found that the underlying substrate with a relaxing layer on top indicated significant distortion that strongly influenced the apparent degree of relaxation. The importance on the most appropriate reflections used for measuring similar volumes is also discussed.