Reciprocal space

All,

There is a well defined definition for these axes. I would always refer to them by the paper which the code is derived. These angles are defined in the paper by:

J. Appl. Cryst. (1993). 26, 706-716    [ doi:10.1107/S0021889893004868 ] Angle calculations for a six-circle surface X-ray diffractometer M. Lohmeier and E. Vlieg
J. Appl. Cryst. (1987). 20, 330-337  Angle Calculations for a Five-Circle Diffraetometer Used for Surface X-ray Diffraction by E. Vlieg et al.

I would strongly suggest being internally consistent with these papers, then change either names or coordinate systems after the io modules.