Typically, a roundness measuring machine will have a motorised turntable and a holder for a measuring probe. It is normally used to measure the roundness of a component such as a crankshaft which is intended to have a circular cross-section. In use, the component is placed on the turntable with its axis co-axial with the axis of rotation of the turntable (known as "the spindle axis"), and the tip of a stylus of a measuring probe or gauge which is mounted on the holder is brought into contact with the surface of the component. The turntable is rotated and the angular position of the turntable together with the output from the measuring gauge are repeatedly logged. The logged data provides detailed information about the precise shape of the cross-section of the component at the level where the stylus tip contacted it. Such data can be processed, for example to provide a measure of the extent to which the shape of the cross-section has waveform undulations rather than being truly circular.