Abstract <p>A methodology is presented for experimental studies on residual stresses occurring within the surface layer in the annular grooves of critical-purpose body parts obtained by machining. It is noted that the effect of technological conditions exerted on the qualitative parameters of the surface layer in the course of machining, such as residual stresses, strengthening, and surface roughness, as applied to deep unloading slots, is poorly studied. In order to obtain correct investigation results, a design of model reference samples is proposed and the rationale for the selected calculation and experimental method for determining residual stresses is justified. The results of the studies on residual stresses obtained upon unloading model samples with the use of the experimental installation of JSC SPC TsNIITMASh through the recalculation of the measured displacements into stresses are presented.</p>