Happy World Metrology Day: A Change to SI Units

Metrology Day 2019 Change to Kilogram SI Units

Effective on this World Metrology Day (May 20, 2019), the International System of Units is now based on a set of definitions each linked to the laws of physics.

Given this change to the International System of Units (SI), we now have the advantage of being able to embrace further improvements in measurement science and technology to meet the needs of future users for many years to come.

While the SI has changed a number of times since formal adoption in 1960, redefining four units simultaneously is unprecedented. The four revised units are the Kilogram (mass), the Ampere (electrical current), the Kelvin (thermodynamic temperature), and the Mole (amount of substance). Each unit is now based on physical constants which are inherently stable.

These redefinitions will have no impact on the Second (time), the Meter (length), or the Candela (luminous intensity).

These redefinitions will have little to no impact on our ANAB-accredited customers or on industry because only a very small number of accredited labs around the world work at the levels necessary to directly realize these SI units. Technological advancements may reduce costs permitting more laboratories to work at these levels in the future.

For more information on the traceability of calibrations, see AR 2251, ANAB’s accreditation requirements document for calibration laboratories.

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