.. [You1999] H. You. *Angle calculations for a '4S+2D' six-circle diffractometer.*
   J. Appl. Cryst. (1999). **32**, 614-623. `(pdf link)
   <http://journals.iucr.org/j/issues/1999/04/00/hn0093/hn0093.pdf>`__.
  
.. [Busing1967] W. R. Busing and H. A. Levy. *Angle calculations for 3- and 4-circle X-ray
   and neutron diffractometers.* Acta Cryst. (1967). **22**, 457-464. `(pdf link)
   <http://journals.iucr.org/q/issues/1967/04/00/a05492/a05492.pdf>`__.
  
.. [Vlieg1993] Martin Lohmeier and Elias Vlieg. *Angle calculations for a six-circle
   surface x-ray diffractometer.* J. Appl. Cryst. (1993). **26**, 706-716. `(pdf link)
   <http://journals.iucr.org/j/issues/1993/05/00/la0044/la0044.pdf>`__.
  
.. [Vlieg1998] Elias Vlieg. *A (2+3)-type surface diffractometer: mergence of the z-axis and
   (2+2)-type geometries.* J. Appl. Cryst. (1998). **31**, 198-203. `(pdf link)
   <http://journals.iucr.org/j/issues/1998/02/00/pe0028/pe0028.pdf>`__.
  
.. [Willmott2011] C. M. Schlepütz, S. O. Mariager, S. A. Pauli, R. Feidenhans'l and
   P. R. Willmott. *Angle calculations for a (2+3)-type diffractometer: focus
   on area detectors.* J. Appl. Cryst. (2011). **44**, 73-83. `(pdf link)
   <http://journals.iucr.org/j/issues/2011/01/00/db5088/db5088.pdf>`__.