For the convenience of discussion, let's start with physical measurement. Generally speaking, in the physical measurement of length, time and weight, the description of the measurement results is almost uncontroversial. This is because they are direct measurements, and their operation methods or rules (rules) have been accepted by people. As the product of brain-psychology phenomenon, it can't be measured directly, but people's psychology is bound to be shown in people's specific activities and behaviors. If we have a clear operational definition of the subjects such as intelligence or personality characteristics, we can find a set of homework or stimulation (actually a set of tests or questionnaires) to arouse the behaviors of the subjects and infer their intelligence ability or personality characteristics from them. For example, to measure intelligence, we must first find out "what is intelligence" and "which activities are intellectual activities", and then we can determine a set of homework for the subjects to respond to, so as to get his achievement in completing this set of homework, which is his intellectual efficiency. Then we infer his intelligence from the intelligence efficiency directly measured. Therefore, psychological measurement is an indirect measurement.

Educational measurement: it is a quantitative measurement of students' learning ability, academic performance, hobbies, ideology and morality, and many problems in educational measurement. It is mainly used to measure students' psychological characteristics. Educational measurement has the following characteristics: 1, educational measurement is generally indirect measurement; 2. The measurement unit of educational measurement is relative; 3. Educational measurement serves educational purposes; 4. The object of educational measurement is complex.