The idea of the present work was to investigate general features of the vertical travel of the treatment table in different configurations and the limitations of an optimised alignment. The investigations were carried out on two tables for different load cases, lateral positions and turntable angles. A wire was held vertically nearby the rotational axis of the table. The wire was used as reference in the investigations. A digital USB-microscope was attached to the tabletop. An orthogonal set of images of the wire was acquired at different vertical table positions. By analysing the images the vertical travel accuracy of the table was extracted. The two tables were found to travel linearly with the same characteristics over the full range of 110 cm with deviations less than 0.5 mm relative to a straight line. A divergence from a vertical travel above 0.5 mm was found to originate from misalignment. An alignment procedure to attain the optimal vertical performance with a minimum of inclination was presented. This procedure must be relayed on objective measured data of the travel with uncertainties far beyond 0.5 mm. Our suggested experimental method was found to have the potential to obtain the required data.