The diffractometer measurement of twinned and clustered crystals requires an accurate knowledge ofQi=UiBimatrices of single‐crystal individuals contained in the sample. A determination of theQimatrix is best done from several accurately centered orienting reflections diffracted by theith single‐crystal individual. The assignment of the orienting reflections to the individuals is easy for well resolved reciprocal lattices; for closely superimposed ones a method is presented which facilitates this assignm