NIM Completes Recalibration of Hong Kong Gravity Datum

Recently, the gravity research team of the National Institute of Metrology (NIM), China was invited to the Hong Kong Special Administrative Region (Hong Kong SAR) and successfully completed the recalibration of the Hong Kong gravity datum. This effort enables the gravity datum of Hong Kong SAR to be traceable to the national primary standard for gravitational acceleration, ensuring the accuracy and consistency of related measurements.

According to the regulations of the Innovation and Technology Commission of Hong Kong, the calibration of the gravity datum must be carried out using instruments that have participated in key comparisons of the International Committee for Weights and Measures (CIPM), with comparison results included in the Key Comparison Database (KCDB) of the International Bureau of Weights and Measures (BIPM). Furthermore, the team responsible for the measurement must possess internationally recognized Calibration and Measurement Capabilities (CMCs) for gravitational acceleration. The independently developed NIM-3A absolute gravimeter by the gravity research team of NIM has participated in multiple international key comparisons, achieving a combined uncertainty in gravitational acceleration measurement of better than 3 μGal and demonstrating excellent comparison results and equivalence with international standards. The team has two CMCs published in the BIPM KCDB—one for gravity on site and another for absolute gravimeter, with performance reaching world-leading levels. NIM’s technical capabilities fully meet the requirements of the Innovation and Technology Commission of Hong Kong.

The value of gravitational acceleration is a key parameter for force measurement and calibration. The calibrated gravity datum can provide strong metrological support for the calibration and manufacturing of advanced instruments used in force metrology in the Hong Kong SAR, such as piston pressure gauges, force standard machines, and weighing instruments, thereby enhancing the reliability and consistency of regional measurement values.