1-1 Concept of Measurement

According to the recommended basic terminology in international metrology, 'measurement is a set of operations aimed at determining a quantity'. The quantities here all refer to physical quantities. For each physical quantity, it is only a qualitative property shared by some physical objects, such as temperature, mass, length, and so on. Each physical quantity represents a certain aspect of a physical object, and more specifically, each quantity has its quantitative properties such as temperature, mass, length, and so on.  

The measured value of a physical quantity is a name consisting of the numerical value representing the physical quantity and the unit of the physical quantity.  

The same physical quantity may result in different measurement values due to the selection of different units. Therefore, when giving the size of the measurement value, it is necessary to provide the measurement unit used.  

1-2 Measurement Methods

Measurement method is the means used to complete measurement tasks. Generally, the calculations and actual operations involved in measurement are defined based on given principles.  

During the measurement process, various measuring instruments and methods are used due to differences in the measurement object, measurement environment, and measurement parameters.  

1. When using appropriate measuring instruments to directly complete the measurement task and obtain the size of the measured physical quantity with sufficient accuracy, this type of measurement is often referred to as simple measurement.  

2. Directly measuring any measurement involves different simple measurements. If only one simple measurement is included in the measurement process and the size of the measured physical quantity can be obtained by calculating the measurement results based on some known data, this type of measurement is often referred to as direct measurement.  

3. Indirect measurement: If the measurement of the measured physical quantity includes two or more simple measurements, or involves calculating the final measurement result based on several direct measurement results, this measurement is called indirect measurement or indirect measurement.  

1-3 Performance indicators of measuring instruments

The operational characteristics of instruments are usually divided into two categories: static characteristics and dynamic characteristics.