In the case of processes where rolls, rollers or other cylindrical objects are rotated very quickly or an extremely constant radius must be maintained, the radial deviations must be checked before and/or during the process. Eddy current sensors for metallic objects or capacitive or laser triangulation sensors for all other materials are used for this. The sensor measures the rotating roller from one side. A deviation from the required radius is shown by a change in the distance to the sensor. In doing so, the radius is checked with submicrometer precision.