Diffractometric angles for rotation around the diffraction vector

It is shown that the azimuthal angle ψ of rotation around the diffraction vector and the four angles χ₀, χ, φ' and 90 - ω, all belong to one right spherical triangle from which the new relations sin ψ = sin χ sin φ' and cos φ' = cos ω cos ψ are derived. These angles are in fact related by ten trigonometric equations which can also be derived by matrix methods. The setting angles for a full ψ rotation of 360° are easily determined when results of both methods are used together.