The International System of Units (SI) forms the foundation of physical measurements. It defines seven base units, their derived units and prefixes. On November 16, 2018, the 26th meeting of the General Conference on Weights and Measures (CGPM) passed a resolution to revise four of the seven SI base units, namely, the kilogram, the ampere, the kelvin and the mole. The revision brings an end to the use of physical objects to define measurement units by linking all SI base units to physical constants, which guarantees their stability and universality. The adopted changes will be implemented on May 20, 2019, the next World Metrology Day.

The Standards and Calibration Laboratory (SCL), being the official custodian of Hong Kong’s reference measurement standards for physical measurements, has prepared for this change. To promote to the public the revision of SI units and its impact, the SCL has organised a series of events, including metrology workshops and public talks. In addition, a Metrology Symposium will be held to further address the needs of the local testing and certification industry on January 11, 2019.