Roundness Tester Specimen Specimens are available for calibration and the functional check of instruments, specifically studied for roundness testers; upon request calibration certificates are released. In general, three specimens are used on roundness testers: - Specimen sphere or hemisphere in steel or optical glass that allows to quantify and check the plate’s rotary oscillations, and therefore adjust the error - Guizzo specimen that allows to calibrate and check the pick-ups’ sensitivity, through a radial known groove - The specimen cylinder made in steel or granite, that thanks to its utmost cylindricity accuracy, allows to align the column of the roundness testers to the plate’s axis, and to check precision during movement. Salbro Engineers represents SM Metrology Systems for their surface metrology products such as Roundness, Roughness, Contour / Profile measuring machines, accessories and calibration standards / specimens.