Control of single crystal orientation in modern gas turbine components is a critical quality control issue for optimum reliable behaviour, and an increasingly important aspect of trade. This paper reviews industrial practice for the determination of primary crystal orientation and for the determination of 'disorientation' (R-value) between sub-grains. Different techniques and measurement conventions are compared, and the errors of measurement have been assessed through a European round-robin. Causes of poor reproducibility in 'disorientation' measurement have been identified by EBSD investigations. Recommendations for unified practice have been made in a Good Practice Guide as a precursor to a new industry-wide standard.