In all achsiographic techniques a non perpendicular alignment and adjustment of the sagittal-vertical registration plates to the centric positioned hinge axis leads to an incorrect recording of mandibular movements. Among other things the dimension of the registration error decisively depends on the quality and quantity of the angle of hinge axis inclination. The achsiographies of 234 patients were analysed. In most cases incorrect measurements of the individual Bennett angle of only 1-2 degrees were found. These deviations are not relevant and have therefore not to be taken into account. On the other hand differences of the correct and incorrect recorded Bennett angle between 3 degrees and 8 degrees could be registrated in more than 25%. These errors have to be considered in diagnostics and treatment procedures. Correcting methods and techniques are described and discussed.