The precession camera inclines the reciprocal lattice by a small angle (known as μ) so that the reciprocal lattice plane cuts the sphere of reflection. Any lattice point that lies on this intersection circle will give rise to a reflection (for example, the lattice point at the “top” of the circle with the indicated reflection angle 2θ). If the normal to this reciprocal lattice plane is made to rotate about the X-ray beam (i.e., it precesses about the x-ray beam), a series of intersection circles will be traced and a large number of lattice points will pass through the sphere of reflection. The film is kept parallel to this lattice plane, so any reflection spots occuring on it appeared at equal crystal-to-spot distances. In this way, an undistorted picture of reciprocal space is obtained (next page).