A method, particularly suited to large crystals, is described whereby the missetting of a crystal on an oscillation or Weissenberg goniometer may be determined from a single setting photograph. A graphical solution appropriate to the small angles involved is developed. The measurements of the positions of spots on a setting (oscillation) photograph are converted into coordinates of a straight line. From the intercepts of this line on its coordinate axes the angles defining the mis-setting may be determined. A practical example is given.