In many places, you need to ensure that the surfaces are perfectly straight, e. g., when using a lathe, CNC, etc.It is desirable that the tool moves during a straight path to obtain the perfect cylinder and it is possible only when the guiding guideways are themselves straight Line or plane is the basic unit of measurement for most methods of measurement. The standard of straightness in precise engineering is represented by a ruler. According to Bryan’s Principle, a straightness measuring device should be aligned with the functional point at where straightness is to be determined. If this is often difficult, either the slideways that transfer the measurement must not move at an angle or angular motion data should be used to calculate the result of the offset.