These Pyrex® volumetric pipets are calibrated to Class A tolerances in accordance with ASTM E-542, and ASTM E-969. Each pipet is individually serialized and supplied with a Certificate of Identification and Capacity, traceable to NIST standards. These precision pipets are manufactured and calibrated "To Contain" (TC - bottom line) and "To Deliver" (TD - top line) to specifications for Class A volumetric ware. Color-coded markings enameled onto the glass. Now tested and calibrated in an ISO/IEC 17025 certified laboratory.