Standard: Not Traceable or Certified.
NIST Traceable: Serialized and calibrated with instruments traceable to the National Institute of Standards and Technology.
A2LA Accredited and NIST Traceable: Serialized with all calibrations subcontracted to an independent Metrology Laboratory that is certified to 9001:2000 ISO, accredited by A2LA to ISO/IEC 17025 and ANSI/NCSL Z540.1. The Bubble-O-Meters are calibrated in accordance with ASTM E694. Certified uncertainty of 0.25% across any range.