The sphere is a three-dimensional figure, which in many respects strongly resembles the two-dimensional figure of the circle. In geometry, the sphere as a short form refers to both spherical surfaces and spherical bodies. A spherical surface is formed from the area created when a circular line is rotated by one diameter of the circle. All points on the spherical surface have the same distance to the center of the sphere. The spherical surface united with the interior of the sphere is called a spherical body or solid sphere. For metrology, the sphere is of two importance: first, many measurement tasks deal with spheres in the form of DUTs, because these must also be toleranced for roundness, profile, and other factors. Constructions such as ball bearings are only functional if the installed balls meet the corresponding quality requirements. On the other hand, many tactile metrological devices work with balls in their probes, so that metrology itself also depends in many places on designs that rely on high-quality precision balls.