International
Tables for Crystallography Volume C Mathematical, physical and chemical tables Edited by E. Prince © International Union of Crystallography 2006 
International Tables for Crystallography (2006). Vol. C, ch. 5.2, pp. 497498

The types of powder camera frequently used in the determination of lattice parameters are described in Section 2.3.4 . The main geometrical aberrations affecting measurements made with them are summarized in Table 5.2.8.1. At high angles, most of them vary approximately as (π − 2θ)^{2}, and one would thus expect to obtain an approximately straightline extrapolation if the apparent values of the lattice parameter were plotted against a function something like (π − 2θ)^{2}. A function that has been found very satisfactory in practice was suggested by Nelson & Riley (1945a, b) [see also Taylor & Sinclair (1945a, b)]: This function gives linear plots down to quite small values of θ.
^{†}For van Arkel and Bradley–Jay arrangements. For Straumanis–Ievins', + or − and , respectively.

References
Langford, J. I., Pike, E. R. & Beu, K. E. (1964). Precise and accurate lattice parameters by film powder methods. IV. Theoretical calculation of axial (vertical) divergence profiles, centroid shifts, and variances for cylindrical powder diffraction cameras. Acta Cryst. 17, 645–651.Nelson, J. B. & Riley, D. P. (1945a). An experimental investigation of extrapolation methods in the derivation of accurate unitcell dimensions of crystals. Proc. Phys. Soc. London, 57, 160–177.
Nelson, J. B. & Riley, D. P. (1945b). An experimental investigation of extrapolation methods in the derivation of accurate unitcell dimensions of crystals. Proc. Phys. Soc. London, 57, 477–495.
Taylor, A. & Sinclair, H. B. (1945a). The influence of absorption on the shapes and positions of lines in Debye–Scherrer powder photographs. Proc. Phys. Soc. London, 57, 108–125.
Taylor, A. & Sinclair, H. B. (1945b). On the determination of lattice parameters by the Debye–Scherrer method. Proc. Phys. Soc. London, 57, 126–135.