Abstract: A coin testing apparatus (10) comprises a coin passageway, a coin track (13) along which coins pass on their edges through the coin passageway and an inductor (16) adjacent the coin passageway. The inductor is connected in an oscillating circuit (40) so that the inductor (16) produces an oscillating magnetic field in the coin passageway. The frequency of the oscillating circuit is measured using a counter (41). A number representative of the idle frequency is stored in register (44). When a coin passes the inductor (16), the apparatus (10) detects whether the resulting frequency shift corresponds to the shift for an acceptable coin by comparing the difference between the number stored in register (44) and the number stored in counter (41) with a number previously stored in memory (48). The inductor (16) is oblong and has its major axis perpendicular to the track so that the arrangement is sensitive to variations in diameter over a large range of diameters.