This Good Practice Guide describes the determination of single-crystal orientation measurements for single-crystal nickel-base castings by back and side-reflection X-ray diffraction (Laue). These measurements check the quality of the castings against specifications set by the OEMs for the foundries.For quality control three parameters are determined:1. The angle between a reference direction in the component, defining the preferred direction of solidification, and the closest <100> direction. (q).2. Less commonly, the angle between a second reference direction in the plane perpendicular to the original reference direction (a) and/or a <001> direction (k).3. For single crystals with more than one grain a measurement of the misorientation or disorientation between adjacent grains (R).The guide contains information about the definition of orientation parameters; principles of back-reflection and side-reflection Laue systems; calibration standards; system alignment; calibration; validation and uncertainty of measurements with a final section on making the measurements.The definition of primary angles is based upon European practice but a comparison with two definition conventions used in the USA is included.