The redefinition of the International System of Units (SI), approved by the General Conference on Weights and Measures (CGPM) in 2018, opened up a wider scope for the development and application of metrology. Starting from the definition of metrology, this paper analyzes the aspects and elements of metrology by deduction and induction and then puts forward the concept of "dimensions of metrology". The basics of metrology as a science, legal metrology, and application of metrology in industry are explored accordingly. It is proposed that the aspects of the basics of metrology include research on measurement theories, traceability of quantity values, new measurement devices, operational specifications, and analysis of measured values. It is proposed that the basics of metrology and legal metrology constitute a metrological infrastructure that underpins applications of metrology in various industries. Three development stages of metrology are reviewed from the perspective of the dimensions of metrology. The paper also looks ahead at new changes in the Era of Metrology 3.0 that may be brought about by the redefinition of SI.

metrology  /  measurement science  /  legal metrology  /  industrial metrology