Requirements to roundness tolerances are a part of the geometrical product specifications. However, the definition for the roundness tolerance according to ISO 1101 considering radial deviations only is not sufficient to assure the functionality of many products. In addition, the form of roundness deviations along the circumference plays a significant rule for rotating machine components. Especially periodic deviations cause vibrations that lead to noise and wear. The Fourier analysis and the corresponding amplitude spectrum deliver information about the properties of the form derived from the magnitude of the different harmonics. This information presents a series of results depending on the harmonics. Therefore, a dedicated tolerance definition in most cases in from of a mathematical equation is used. The currently used tolerance definitions are not standardized and difficult to understand. Often, only one amplitude of the spectrum is significantly larger than the others are and effects functionality. In this case, an algorithm that detects the largest amplitude enables an easier tolerance definition.