This standard specifies the basic terms and definitions in the field of Instrument, aiming to unify the use of terms. It is applicable to Instrument standard formulation, technical document preparation, textbook and book preparation, and literature translation, etc. The standard covers basic concepts such as measurement quantities, variables, Measurement units and their symbols, including definitions of basic units and derived units, as well as relevant descriptions of magnitude values and true values. It provides a clear explanation of terms and ensures consistent use of terms in various types of literature and standards.