There is an opinion among sociologists of religion that it is impossible to quantify religiosity by the method of polling. The author rejected the extreme agnosticism in relation to measuring the strength of individual faith and considered one of the options for such a method. The famous sociologist-researcher of Orthodoxy V. F. Chesnokova-created an index of churchliness (C-index), which categorizes respondents into five churched groups according to the strongest answer to five main questions about actual religiosity. Additional questions could change the result only in the direction of strengthening the churchliness. Previous critical articles on the C-index have proven incorrect. Now is the time to make an attempt to fix this toolkit. In order to avoid overestimating the number of deeply believers, it is proposed to reconstruct the logical foundations of the aforementioned method of measuring the degree of Orthodox religiosity. Instead of a clear affiliation with one of the five groups in accordance with actual religiosity, a vague affiliation with a single Orthodox group was proposed on the basis of comparing actual religiosity with the normative one. Various variants of the membership function are considered. The requirements for this element of the sociological methodology have been developed: it must, firstly, be mathematically correct, and secondly, implement the following proposition: the closer to each other the arguments of the function (i.e., the more the concrete x and the abstract y modality correspond to each other), the greater the value of the function, the furtherthe less. For all criteria, the membership function () = 1 − | − | is applied. A profound modernization of the approach to empirical quantification of the degree of Orthodox religiosity has made it possible to create an innovative toolkit for measuring the number of believers.