A ribbon controller is a tactile sensor used to control synthesizers. It generally consists of a resistive strip that acts as a potentiometer. Because of its continuous control, ribbon controllers are often used to produce glissando effects. Early examples of the use of ribbon controllers in a musical instrument are in the Ondes Martenot and Trautonium. In some early instruments, the slider of the potentiometer was worn as a ring by the player. In later ribbon controllers, the ring was replaced by a conductive layer that covered the resistive element.