Specialized measuring instrument for high-precision measurement of roundness (geometric accuracy of circular shape) of cylindrical parts and rotating bodies. Used for quality control by quantifying deviations from true roundness (ellipticity, polygonal shape, waviness) in machined products such as bearings, shafts, pipes, and ring components. Applied in finish accuracy verification of lathe-machined products, quality inspection of automotive parts, and incoming inspection of precision mechanical components, detecting minute circular shape distortions that cannot be detected by general length measuring instruments. Primarily uses contact probe rotation measurement method with graphical display of measurement results.