1. Wrong interpretation
The error is the measured value minus the reference value. The measured value is referred to as the measured value for short, which represents the value of the measured result. The so-called reference quantity is generally expressed by the true value or agreed quantity of the dosage. For measurement, people often take the true size of a quantity as the true value measured during observation.
It is actually an ideal concept. Because only "when a quantity is perfectly determined and all defects in measurement can be eliminated, the quantity obtained through measurement" is the real value of quantity. From a measurement point of view, it is difficult to do this. So generally speaking, it is impossible to know the true value exactly.
2. Definition
The difference between the observed value or calculated value of a quantity and its true value refers to statistical error, that is, the number of times a quantity deviates from the standard value or specified value due to some errors or usually due to some uncontrollable factors in the process of measurement, calculation or observation. Mathematically, the difference between the measured value or other approximate value and the true value is called error.
According to junior high school physics textbooks, error refers to the difference between the measured value and the real value when measuring physical quantities such as length and time, which is limited by the instruments and measurement methods used.
3. System error
The main sources are as follows: instrument error: it is caused by the inaccuracy of the instrument itself. Method error: It is caused by the analysis method itself. Reagent error: caused by impurities in distilled water or impure reagents. Operation error: it is caused by the operator's immature conditions for mastering the analysis operation, insensitivity of personal observation organs and inherent habits. Subjective error: It is caused by the operator's subjective reasons, such as the defect of observation and judgment ability or bad habits.
4. Accidental error
Under the same conditions, when measuring the same physical quantity for many times, due to various accidental factors, the measured value will sometimes be too large and sometimes too small. This kind of error is called accidental error.
There are many reasons for accidental errors, such as incorrect line-of-sight position, inaccurate measuring point position, slight changes of experimental instruments due to environmental temperature, humidity, unstable power supply voltage, vibration and so on. The influence of these factors is generally small, and it is difficult to determine the specific influence of a certain factor, so it is difficult to find out the causes of accidental errors and eliminate them.