For almost 25 years, mankind has been dealing with the problems of estimating measurement uncertainty. When applying uncertainty, the goal is not to determine the true value during the measurement as far as possible. That is, it is recognized that the information obtained during the measurement allows only to assign a reasonable interval of values for the measured value, based on the assumption that no errors were made during the measurement. However, even the most accurate measurements cannot reduce this interval to a single value due to the finite number of details in the description of the measured value. An interval can be represented by a single value of its own, called the «measured value of the quantity». Over the years, many scientific works have been devoted to methods of estimating the uncertainty of measurements. At the same time, the main conclusion is that the value of uncertainty depends on the applied method of its assessment. In practice, the use of uncertainty has not been widely used. Accredited calibration and testing laboratories must be able to estimate measurement uncertainty. Therefore, they learn uncertainty assessment methods, develop examples. It is written in the management system that the evaluation of the uncertainty of the measurement result is provided at the request of the customer. But neither the customer nor the executor understands the purpose of its application. Therefore, now is the time for scientists, together with practitioners, to deal with the issue of establishing target uncertainty for solving specific measurement tasks, such as establishing compliance of products with specified requirements, establishing the suitability of measuring equipment after calibration, etc. Thus, for practical application, it is important to be able to determine the value of the target uncertainty - the value of uncertainty for the measured value of the quantity at which the measured value can be considered reliable for a specific practical application