Contributions to the radial distance uncertainty come from the uncertainty of the overall position of the fitted co-ordinate frame, the uncertainty of the absolute distance to the cylinder-axis, and the uncertainties of the original relative co-ordinates (transducer deflections) of the roundness and straightness measurements. The uncertainty of a single profile measurement point can be estimated to 0,015 µm maximum. Taking this value and the position uncertainties of the generatrices into account, an overall uncertainty of 0,045 µm for the 3D-cylinder radii co-ordinates results.