Pedals for harp tuning were first introduced in 1697. The mechanical action of the pedals changes the pitches of the strings. The seven pedals each affect the tuning of all strings of one pitch-class. The pedals, from left to right, are D, C, B on the left side and E, F, G, A on the right. Each pedal attaches to a rod or cable in the column of the harp, which connects to a mechanism in the neck. When the player presses a pedal, small discs at the top of the harp rotate. The discs are studded with two pegs that pinch the string as they turn, shortening its vibrating length. In each position the pedal can be secured in a notch so the foot does not have to continuously hold it in position (unlike piano pedals).