Certified Reference Materials (CRM) meet federal, state, and local requirements, providing standardized reference calibration for pH meters. Produced in compliance with ISO/IEC 17025:2017, ISO 17034:2016, ISO Guide 31, and ISO 33405, CRMs ensure top-tier accuracy, documentation, and standards. They undergo extensive stability, transportation, and repeatability testing, with uncertainty (U) assigned from these evaluations. Calibration reports are issued by an ISO 17034 and ISO 17025 accredited lab. Environmental Express Oakton monitors the solution over 1 to 2 years and informs users of any changes.