A customizing method includes steps which consist in: a) determining on the basis of a circuit model, a set of vectors each corresponding to a theoretical operating time of the circuit when a predetermined sequence of tests is applied, the coefficients of each vector representing the state of a common set of elements of the circuit among which the element to be customized (12); b) defining on the basis of a comparison of vectors, a composite of logic operators applied on the vectors and enabling to extract the coefficient corresponding to the element to be customized (30); c) producing images of the operating circuit at times corresponding to the vectors whereon is applied the composite of logic operators (32); and d) graphically combining the images produced in accordance with a composite of graphic operators corresponding to the composite of logic operators (36).