Bullet_point: ['Each tube has a unique serial number to ensure tracability and also has a sand spot to write on', 'Graduated marks are etched permanently and filled with ceramic to improve visability and to ensure durability', 'In addition to our factory volumetric calibration, LK Industries offers gravametric calibrations at competetive pricing. Our tube are the most accurate on the market', 'Tubes are rigorously tested for adherence to ASTM and API standards. We also use magnifying techniques to ensure there is no weakness in the glass prior to production', 'Tubes conform to ASTM & API standards, meaning they can be used in most regulatory environments'] (Page 1)