AbstractX-ray diffraction provides an easy and powerful method for measuring residual stress in thin films. However, nonlinearity of the d vs. sin2ψ relation can lead to the misinterpretation of results, especially when one of the measurements is made at low values of ψ relation for different combinations of ideal crystallographic textures and grain shapes are given. In all cases, a high ψ angle range exists where the d vs. sin2ψ relation in the low ψ angle range.