The assessment of measurement uncertainty is a very important task in our metrological verification work. It is an indispensable and crucial part of the metrological standard evaluation process.  Therefore, as metrological verification personnel, it is extremely necessary to have a thorough understanding and mastery of uncertainty and its assessment.  However, many comrades, especially those who are a bit older, are quite unfamiliar with uncertainty. They find it very difficult to deal with such issues. Based on the written definition formulas, they find it hard to understand the practical significance of measuring uncertainty, let alone the assessment work of uncertainty.  Therefore, it is highly necessary to provide some simple explanations and clarifications on measurement uncertainty and the evaluation of measurement uncertainty of measuring instruments.  Let's briefly explain what measurement uncertainty is.  The definition of measurement uncertainty is: "A parameter associated with the measurement result that characterizes the dispersion of the values reasonably assigned to the measured quantity."  Here, the term "reasonable" refers to the fact that our measurement process is carried out under controlled conditions. It is not a casual process. It is a measurement process controlled under a series of effective conditions, such as the normal operation of the measuring equipment under effective environmental conditions, within an effective verification period, and the regular operation of qualified inspection and testing personnel.  The "dispersion" here refers to the degree of inconsistency among the measurement results that exist in a certain area.  

Uncertainty refers to the degree of uncertainty; in other words, it is the credibility of the measurement results.  The greater the uncertainty, the less reliable the measurement results will be.  The smaller the uncertainty, the greater the credibility of the measurement result.  For instance, we say a weight weighs 200g. The measurement result we get from it is 200.05g. 200.05g is our measurement result relative to this weight.  But is this "200.05g" the true mass of this pencil?  As we all know, all measurement behaviors have measurement errors, which come from many aspects, including personnel, equipment, environment and a series of other factors, all of which will affect the measurement results.  Therefore, "200.05g" is not the actual mass of this weight; it is merely an approximate value relative to its true value.  So, how can the true value of this weight be characterized?  So we introduced the concept of uncertainty. Through a series of measurements and calculations, we obtained a set of data: the mass of this weight can be expressed as: (2000.1g±0.05g, with a confidence probability of 95%), that is, the mass of this weight is between 200.05 and 200.15g, with a 95% certainty.  It is to give us the existence range of the true value of this weight and also inform us of its reliability.  That is to say, there is a 95% chance that the true mass of this weight is between 200.05 and 200.15 grams, thus achieving a result that is very close to the true value.  The above representation is the measurement result of the weight expressed in terms of uncertainty.  So, the question arises: How do we obtain the above data?  This involves the assessment of the uncertainty of the measurement results. When we assess the uncertainty of the measured quantity, we will obtain the corresponding results.