Abstract. In this article, we present a new metric called the comparative uncertainty, according to which the least achievable relative uncertainty is calculated when measuring the Planck constant. To calculate the comparative uncertainty, information theory is used. The optimizing criterion is the number of quantities considered in the model. Its calculation is possible due to the fact that any model contains a certain amount of information about the object under study. Comparative uncertainty can be verified by field trials or computer simulations within a specified range of changes of the Planck constant. The concept of introduced uncertainty is universal and can be recommended for estimating the accuracy of measurements in the study of physical phenomena and technological processes. Examples of application of the proposed approach are discussed.