Geometry and axes are important for multigrain crystallography experiment. You need to know how is your experiment relative, how are you rotating, what are x, y, z axes ?

The figure below gives an outline of a typical definition of laboratory axes and angles

More precise and detailed calculations are available in this file, extracted from the fable project: fable_geometry_version_1.0.8.pdf.

Because of the way data is saved in image files, there are always confusions with the orientation of detector images. They can be flipped in any way you can think of.

Here is an example, taken from an old Fable manual (Note: one of the example is wrong, I did see that some times ago, seb)

Again, more precise definitions and calculations can be found in a former Fable manual: fableimageorientdoc_0.5.pdf