The linear error motion includes the flatness / straightness of a positioner or motion system. They describe the parasitic displacement from an ideal straight line in the axis perpendicular to the direction of motion. The flatness and straightness are evaluated over the full travel range and are defined as the maximum displacement in vertical (flatness) and horizontal (straightness) direction. In kinematic system, the flatness and straightness are measured in each degree-of-freedom, separately.