The discovery of a new coefficient named “Radicular Spectral Attenuation Coefficient-RSAC”, applicable in electronic foramen locators is described. The novelty is the use of the spectral attenuation of a multifrequency electrical current signal, applied through the endodontic file into the tooth canal (TC), to determine the root length and the foramen position. FIG. (2): (2.1), (2.4), (2.8) and (2.2), (2.5), (2.9) are the amplitude and frequency axes, respectively; (2.3) is the electrical current frequency spectrum applied into the TC; (2.6) shows the spectrum exponential decay (2.7) of the signal measured over the TC. In (2.10) the axes (2.4) and (2.5) were logaritmized to linearize the exponential decay. The RSAC is the average inclination of the line (2.11), which is proportional to the distance between the tip of the endodontic file and the apical foramen. The RSAC changes as the tip of the file gets near the foramen.