International
Tables for Crystallography Volume F Crystallography of biological macromolecules Edited by E. Arnold, D. M. Himmel and M. G. Rossmann © International Union of Crystallography 2012 
International Tables for Crystallography (2012). Vol. F, ch. 2.1, p. 56
Figure 2.1.4.9^{a}Laboratory of Biophysical Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands 

Figure 2.1.4.9
Xray diffraction by a crystal is, in Bragg's conception, reflection by lattice planes. The beams reflected by successive planes have a path difference of , where d is the latticeplane distance and θ is the reflecting angle. Positive interference occurs if , , etc., where λ is the Xray wavelength. Reproduced with permission from Drenth (1999). Copyright (1999) SpringerVerlag. 