Abstract: The coin rolls on a track of triangular section with a vertical side and an oblique side, in which it penetrates as a function of its thickness. The difference in time between the beginnings (or ends) of occultation of the upper cells determines the mean speed and from the duration of this occultation is deduced the length of the chord (PQ) at the upper level (Y-Y'). Knowing the mean speed, the cell of the second level (Z-Z') makes it possible to determine the corresponding chord (RS). From (PQ) and (RS) are deduced the heights (h.sub.1, h.sub.2) above the plane of roll (X-X') and the diameter and thickness of the coin may then be calculated. More simply, (PQ) and (RS) may be compared electronically with recorded values to reject the coin or accept it and possibly record its value.