The X-ray diffraction method for nondestructively measuring residual stresses in metals is advantageous as it does not require a zero stress condition. With the use of a portable X-ray machine and the back reflection film technique, the method becomes even more useful for measuring stresses in components as the component size is no longer a limitation. This paper discusses the fundamentals, basic techniques, and the type of equipment commonly associated with the portable film technique.Bragg's law and its application to residual stress measurements are presented. The single exposure approach for the portable film technique is contrasted with the double exposure method that is commonly employed with the direct-reading diffractometers. The necessity for determining the stress factor for each material and heat treatment is presented.This technique was applied to measuring residual stresses in three 7079-T6 forgings. The purpose of the program was to determine a manufacturing process sequence that would minimize harmful residual stresses in the machined forgings.