In the United States, there are two sets of accreditation standards for calibration laboratories. ANSI Z540 is shorthand for one of them. Calibration laboratories test measurement and testing equipment and control instruments for diagnostic and standards compliance purposes.
From 1994 to 2000, U.S. national standards for calibration laboratory accreditation were set out in the American National Standards Institute standard, ANSI/NCSL Z540-1-1994, “Calibration Laboratories and Measuring and Testing Equipment – General Requirements." These standards have been updated twice since 2000. The current standard is ANSI/NCSL Z540-3-2006. In common usage, this standard is often shortened to ANSI Z540 or NCSL Z540. ANSI developed ANSI Z540 in collaboration with NCSL, the National Conference of Standards Laboratories.
In 2000, ANSI adopted ISO/IEC 17025, a set of international laboratory calibration accreditation standards. These were developed by the International Standardization Organization and the International Electrotechnical Commission. ISO/IEC 17025 was revised in 2005 to address stricter quality management requirements.
U.S. calibration laboratories can be accredited as ANSI/NCSL Z540 compliant, ISO/IEC 17025 compliant or both. The choice largely depends on the requirements of laboratory clients.