Vibrating reed frequency meter

The image shown is of a vibrating reed type frequency meter. As the name suggests it has reeds which vibrates to indicate the input frequency. Each reed has its own natural frequency. When the input current is supplied every reed vibrates but the reed with natural frequency closest to the incoming frequency vibrates the most. This is mainly used for AC frequency measurement and at the places where accuracy is not a factor. It is cheap as compared to other kinds of frequency meters.