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. 2.2, pp. 3435

Upperlayer photographs are usually recorded in equiinclination geometry [i.e. μ = −ν in equations (2.2.3.7) and (2.2.3.8)]. The Xraybeam direction is made coincident with the generator of the cone of the diffracted beam for the layer concerned, so that the incident and diffracted beams make equal angles (μ) with the equatorial plane, where The screen has to be moved by an amount where s is the screen radius. If the cassette is held in the same position as the zerolayer photograph, then reflections produced by the same orientation of the crystal will be displaced relative to the zerolayer photograph. This effect can be eliminated by initial translation of the cassette by .