This unique standard provides measurement traceability for roughness in both a vertical and circumferential direction. Calibration standard for circumferential and vertical roughness. Traceable international standards. Vertical - Ra 0.35 µm (13.78 µin) Rz 1 µm (39.37 µin) Circumferential - Ra 0.35 µm (13.78 µin) Rz 1 µm (39.37 µin)