International
Tables for Crystallography Volume F Crystallography of biological macromolecules Edited by M. G. Rossmann and E. Arnold © International Union of Crystallography 2006 
International Tables for Crystallography (2006). Vol. F, ch. 11.5, pp. 241242
https://doi.org/10.1107/97809553602060000678 Appendix A11.5.1. Partiality model (Rossmann, 1979; Rossmann et al., 1979)^{a}Department of Biological Sciences, Purdue University, West Lafayette, IN 479071392, USA 
Small differences in the orientation of domains within the crystal, as well as the cross fire of the incident Xray beam, will give rise to a series of possible Ewald spheres. Their extreme positions will subtend an angle 2m at the origin of the reciprocal space, and their centres lie on a cusp of limiting radius , where m is the halfangle effective mosaic spread. As the reciprocal lattice is rotated around the axis (Oy) perpendicular to the mean direction of the incident radiation (Oz), a point P will gradually penetrate the effective thickness of the reflection sphere (Fig. A11.5.1.1). Initially, only a few domain blocks will satisfy Bragg's law, but upon further rotation the number of blocks that are in a reflecting condition will increase. The maximum will be reached when the point P has penetrated halfway through the sphere's effective thickness, after which there will be a decline of the crystal volume able to diffract.
Let q be a measure of the fraction of the path travelled by P between the extreme reflecting positions and , and let p be the fraction of the energy already diffracted. Then the relation between p and q must have the general form shown in Fig. A11.5.1.2. It is physically reasonable to assume that the curve for p is tangential to at and to at .
A reasonable approximation to the above conditions can be obtained by considering the fraction of the volume of a sphere removed by a plane a distance q from its surface (Fig. A11.5.1.2). It is easily shown that if p is the volume, then This curve is shown in Fig. A11.5.1.2 and corresponds to assuming that the reciprocallattice point is a sphere of finite volume cutting an infinitely thin Ewald sphere. Also shown in Fig. A11.5.1.2 is the line which would result if the reciprocallattice point were a rectangular block whose surfaces were parallel and perpendicular to the Ewald sphere at the point of penetration.
Assuming a righthanded coordinate system (x, y, z) in reciprocal space fixed to the camera, it is easily shown (Wonacott, 1977) that the condition for reflection is where is the distance of a reciprocallattice point P(x, y, z) from the origin, O, of reciprocal space. Similarly, it can be shown that at the ends of the path of the reciprocallattice point through the finite thickness of the sphere, Therefore, Since δ is small, it can be assumed that is independent of the position of the reciprocallattice point P between the extreme positions and (Fig. A11.5.1.1). Hence, the length of the path through the finite thickness of the sphere is proportional to Now, if a reflection is only just penetrating the sphere at the end of the oscillation range, then the fraction of penetration is given by Substituting this expression into equation (A11.5.1.4), it follows that where and The subscripts A and B refer to the beginning and end of the oscillation range for the partial reflection P, respectively.
Similarly, if a reflection is almost completely within the sphere, There are indeed four such conditions: two while a reflection is entering the Ewald sphere, and two while it is exiting. As such, it is readily seen that is the range for a partial reflection. The full range of conditions is given in Table A11.5.1.1, as are the conditions for a full reflection.

References
Rossmann, M. G. (1979). Processing oscillation diffraction data for very large unit cells with an automatic convolution technique and profile fitting. J. Appl. Cryst. 12, 225–238.Rossmann, M. G., Leslie, A. G. W., AbdelMeguid, S. S. & Tsukihara, T. (1979). Processing and postrefinement of oscillation camera data. J. Appl. Cryst. 12, 570–581.
Wonacott, A. J. (1977). Geometry of the oscillation method. In The rotation method in crystallography, edited by U. W. Arndt & A. J. Wonacott, pp. 75–103. Amsterdam: North Holland.